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Ligand optimization of exchange interaction in Co(II) dimer single molecule magnet by machine learning

DOI10.24435/materialscloud:pe-zv

Sijin Ren, Eric Fonseca, William Perry, Hai-Ping Cheng, Xiao-Guang Zhang, Richard Hennig

  • This record contains data structures used in the manuscript titled Ligand optimization of exchange interaction in Co(II) dimer single molecule magnet by machine learning. Designing single-molecule magnets (SMMs) for potential applications in quantum computing and high-density data storage requires tuning their magnetic properties, especially the strength of the magnetic interaction. These properties can be characterized by first-principles calculation based on density functional theory (DFT). In this work, we study the experimentally synthesized Co(II) dimer SMM with the goal to control the exchange energy between the Co atoms through tuning of the capping ligands. The experimentally synthesized Co(II) dimer molecule has a very small exchange energy (< 1meV). We assemble a DFT dataset of 1081 ligand-substitutions for the Co(II) dimer. The ligand exchange provides a broad range of exchange energies from +50 meV to -200 meV, with 80% of the ligands yielding a small exchange ...

Latest version: v1
Publication date: Dec 07, 2021


Polymer descriptor data set for machine learning prediction of specific heat

DOI10.24435/materialscloud:43-js

Rahul Bhowmik, Sangwook Sihn, Ruth Pachter, Jonathan Vernon

  • We have developed a polymer descriptor data set from the existing data. The data set has 188 descriptors which describe polymer atomic and molecular behavior. The descriptors are mapped to the specific heat of polymers using supervised and unsupervised machine learning approaches. The mapping helps predict the specific heat of polymers at room temperature. The descriptor data set is useful in synthesizing novel polymers with desired heat capacities.

Latest version: v2
Publication date: Dec 06, 2021


Ab initio modeling of thermal transport through van der Waals materials

DOI10.24435/materialscloud:7y-1a

Sara Fiore, Mathieu Luisier

  • An advanced modeling approach is presented to shed light on the thermal transport properties of van der Waals materials (vdWMs) composed of single-layer transition metal dichalcogenides (TMDs) stacked on top of each other with a total or partial overlap only in the middle region. It relies on the calculation of dynamical matrices from first principles and on their usage in a phonon quantum transport simulator. We observe that vibrations are transferred microscopically from one layer to the other along the overlap region which acts as a filter selecting out the states that can pass through it. Our work emphasizes the possibility of engineering heat flows at the nanoscale by carefully selecting the TMD monolayers that compose vdWMs.

Latest version: v2
Publication date: Dec 06, 2021


Unidirectional Kondo scattering in layered NbS2

DOI10.24435/materialscloud:n0-cs

Edoardo Martino, Carsten Putzke, Markus König, Philip J. W. Moll, Helmuth Berger, David LeBoeuf, Maxime Leroux, Cyril Proust, Ana Akrap, Holm Kirmse, Christophe Koch, ShengNan Zhang, QuanSheng Wu, Oleg V. Yazyev, László Forró, Konstantin Semeniuk

  • Crystalline defects can modify quantum interactions in solids, causing unintuitive, even favourable, properties such as quantum Hall effect or superconducting vortex pinning. Here we present another example of this notion—an unexpected unidirectional Kondo scattering in single crystals of 2H-NbS2. This manifests as a pronounced low-temperature enhancement in the out-of-plane resistivity and thermopower below 40 K, hidden for the in-plane charge transport. The anomaly can be suppressed by the c-axis-oriented magnetic field, but is unaffected by field applied along the planes. The magnetic moments originate from layers of 1T-NbS2, which inevitably form during the growth, undergoing a charge-density-wave reconstruction with each superlattice cell (David-star-shaped cluster of Nb atoms) hosting a localized spin. Our results demonstrate the unique and highly anisotropic response of a spontaneously formed Kondo-lattice heterostructure, intercalated in a layered conductor.

Latest version: v1
Publication date: Dec 06, 2021


Electron correlation enhances orbital polarization at a ferromagnetic metal/insulator interface

DOI10.24435/materialscloud:a5-5v

Shoya Sakamoto, Masahito Tsujikawa, Masafumi Shirai, Kenta Amemiya, Shinji Miwa

  • The Fe(CoB)/MgO interface is vital to spintronics as it exhibits the tunneling magnetoresistance (TMR) effect and interfacial perpendicular magnetic anisotropy (PMA) simultaneously. To further enhance TMR and PMA for the development of high-density magnetoresistive random access memory, it is essential to clarify the behavior of Fe atoms interfaced with MgO. This study reveals that the spin and orbital magnetic moments of Fe are enhanced at the Fe/MgO interface. The enhancement in the orbital magnetic moment is much more significant than that predicted by the standard density functional theory. Theoretical calculations based on the orbital polarization correction reproduce this enhancement, the origin of which is attributed to the electron-electron correlation resulting from electron localization at the Fe/MgO interface. The present findings highlight the importance of electro--electron correlation at ferromagnet/oxide interfaces, which has often been disregarded in spintronics, and provide a new perspective in materials design.

Latest version: v1
Publication date: Dec 06, 2021


Phase equilibrium of liquid water and hexagonal ice from enhanced sampling molecular dynamics simulations

DOI10.24435/materialscloud:1g-kb

Pablo M. Piaggi, Roberto Car

  • We study the phase equilibrium between liquid water and ice Ih modeled by the TIP4P/Ice interatomic potential using enhanced sampling molecular dynamics simulations. Our approach is based on the calculation of ice Ih-liquid free energy differences from simulations that visit reversibly both phases. The reversible interconversion is achieved by introducing a static bias potential as a function of an order parameter. The order parameter was tailored to crystallize the hexagonal diamond structure of oxygen in ice Ih. We analyze the effect of the system size on the ice Ih-liquid free energy differences, and we obtain a melting temperature of 270 K in the thermodynamic limit. This result is in agreement with estimates from thermodynamic integration (272 K) and coexistence simulations (270 K). Since the order parameter does not include information about the coordinates of the protons, the spontaneously formed solid configurations contain proton disorder as expected for ice Ih.

Latest version: v1
Publication date: Dec 06, 2021


Quantum electronic transport across ‘bite’ defects in graphene nanoribbons

DOI10.24435/materialscloud:3v-0q

Michele Pizzochero, Kristiāns Čerņevičs, Gabriela Borin Barin, Shiyong Wang, Pascal Ruffieux, Roman Fasel, Oleg V. Yazyev

  • On-surface synthesis has recently emerged as an effective route towards the atomically precise fabrication of graphene nanoribbons (GNRs) of controlled topologies and widths. However, whether and to what degree structural disorder occurs in the resulting samples is a crucial issue for prospective applications that remains to be explored. Here, we experimentally visualize ubiquitous missing benzene rings at the edges of 9-atom wide armchair nanoribbons that form upon cleavage of phenyl groups in the precursor molecules. These defects are referred to as ‘bite’ defects. First, we address their density and spatial distribution on the basis of scanning tunnelling microscopy and find that they exhibit a strong tendency to aggregate. Next, we explore their effect on the quantum charge transport from first-principles calculations, revealing that such imperfections substantially disrupt the conduction properties at the band edges. Finally, we generalize our theoretical findings to wider ...

Latest version: v1
Publication date: Dec 03, 2021


Prediction of phonon-mediated superconductivity with high critical temperature in the two-dimensional topological semimetal W2N3

DOI10.24435/materialscloud:ya-e0

Davide Campi, Simran Kumari, Nicola Marzari

  • Two-dimensional superconductors attract great interest both for their fundamental physics and for their potential applications, especially in the rapidly growing field of quantum computing. In this, we predict a remarkably high superconducting critical temperature of 21 K in the easily exfoliable, topologically nontrivial 2D semimetal W2N3. Furthermore we study how strain and doping can affect its superconducting properties.

Latest version: v1
Publication date: Dec 03, 2021


Unconventional transverse transport above and below the magnetic transition temperature in Weyl semimetal EuCd₂As₂

DOI10.24435/materialscloud:4f-n7

Yang Xu, Lakshmi Das, Junzhang Ma, Changjiang Yi, Simin Nie, Youguo Shi, Apoorv Tiwari, Stepan Tsirkin, Titus Neupert, Maria Medarde, Ming Shi, Johan Chang, Tian Shang

  • As exemplified by the growing interest in the quantum anomalous Hall effect, the research on topology as an organizing principle of quantum matter is greatly enriched from the interplay with magnetism. In this vein, we present a combined electrical and thermoelectrical transport study on the magnetic Weyl semimetal EuCd₂As₂. Unconventional contribution to the anomalous Hall and anomalous Nernst effects were observed both above and below the magnetic transition temperature of EuCd₂As₂, indicating the existence of significant Berry curvature. EuCd₂As₂ represents a rare case in which this unconventional transverse transport emerges both above and below the magnetic transition temperature in the same material. The transport properties evolve with temperature and field in the antiferromagnetic phase in a different manner than in the paramagnetic phase, suggesting different mechanisms to their origin. Our results indicate EuCd₂As₂ is a fertile playground for investigating the interplay ...

Latest version: v1
Publication date: Dec 02, 2021


Molecular vibration explorer: an online database and toolbox for surface-enhanced frequency conversion, infrared and Raman spectroscopy

DOI10.24435/materialscloud:p7-w6

Zsuzsanna Koczor-Benda, Philippe Roelli, Christophe Galland, Edina Rosta

  • We present Molecular Vibration Explorer, a freely accessible online database and interactive tool for exploring vibrational spectra and tensorial light-vibration coupling strength of a large collection of thiolated molecules. The `Gold' version of the database gathers the results from density functional theory calculations on 2'800 commercially available thiol compounds linked to a gold atom, with the main motivation to screen the best molecules for THz and mid-infrared to visible upconversion. Additionally, the `Thiol' version of the database contains results for 1'900 unbound thiolated compounds.They both provide access to a comprehensive set of computed spectroscopic parameters for all vibrational modes of all molecules in the database. Infrared absorption, Raman scattering and vibrational sum- and difference frequency generation cross sections can be simultaneously investigated by the user. Molecules can be screened for various parameters in custom frequency ranges, such as ...

Latest version: v1
Publication date: Dec 01, 2021


Heteroatom oxidation controls singlet-triplet energy splitting in singlet fission building blocks

DOI10.24435/materialscloud:m1-dg

J. Terence Blaskovits, Maria Fumanal, Sergi Vela, Yuri Cho, Clémence Corminboeuf

  • Singlet fission (SF) is a promising multiexciton-generating process. Its demanding energy splitting criterion - that the S1 energy must be at least twice that of T1 - has limited the range of materials capable of SF. We propose heteroatom oxidation as a robust strategy to achieve sufficient S1/T1 splitting, and demonstrate the potential of this approach for intramolecular SF.

Latest version: v1
Publication date: Dec 01, 2021


The AiiDA-Spirit plugin for automated spin-dynamics simulations and multi-scale modelling based on first-principles calculations

DOI10.24435/materialscloud:9s-tx

Philipp Rüßmann, Jordi Ribas Sobreviela, Moritz Sallermann, Markus Hoffmann, Florian Rhiem, Stefan Blügel

  • Landau-Lifshitz-Gilbert (LLG) spin-dynamics calculations based on the extended Heisenberg Hamiltonian is an important tool in computational materials science involving magnetic materials. LLG simulations allow to bridge the gap from expensive quantum mechanical calculations with small unit cells to large supercells where the collective behavior of millions of spins can be studied. In this work we present the AiiDA-Spirit plugin that connects the spin-dynamics code Spirit to the AiiDA framework. AiiDA provides a Python interface that facilitates performing high-throughput calculations while automatically augmenting the calculations with metadata describing the data provenance between calculations in a directed acyclic graph. The AiiDA-Spirit interface thus provides an easy way for high-throughput spin-dynamics calculations. The interface to the AiiDA infrastructure furthermore has the advantage that input parameters for the extended Heisenberg model can be extracted from ...

Latest version: v1
Publication date: Dec 01, 2021


Graphene nanoribbons with mixed cove-cape-zigzag edge structure

DOI10.24435/materialscloud:48-0e

Prashant P. Shinde, Jia Liu, Thomas Dienel, Oliver Gröning, Tim Dumslaff, Markus Mühlinghaus, Akimitsu Narita, Klaus Müllen, Carlo A. Pignedoli, Roman Fasel, Pascal Ruffieux, Daniele Passerone

  • A recently developed bottom-up synthesis strategy enables the fabrication of graphene nanoribbons with well-defined width and non-trivial edge structures from dedicated molecular precursors. Here we discuss the synthesis and properties of zigzag nanoribbons (ZGNRs) modified with periodic cove-cape-cove units along their edges. Contrary to pristine ZGNRs, which show antiferromagnetic correlation of their edge states, the edge-modified ZGNRs exhibit a finite single particle band gap without localized edge states. We report the on-surface synthesis of such edge-modified ZGNRs and discuss tunneling conductance dI/dV spectra and dI/dV spatial maps that reveal a noticeable localization of electronic states at the cape units and the opening of a band gap without presence of edge states of magnetic origin. A thorough ab initio investigation of the electronic structure identifies the conditions under which antiferromagnetically coupled, edge-localized states reappear in the electronic ...

Latest version: v1
Publication date: Dec 01, 2021


Navigating the Ti-C-O and Al-C-O ternary systems through theory-driven discovery

DOI10.24435/materialscloud:3y-h6

Joseph R. Nelson, Richard J. Needs, Chris J. Pickard

  • Computational searches for new materials are naturally turning from binary systems, to ternary and other multicomponent systems, and beyond. Here, we select the industrially-relevant metals Ti and Al and report the results of an extensive structure prediction study on the ternary titanium-carbon-oxygen (Ti-C-O) and aluminium-carbon-oxygen (Al-C-O) systems. We map out for the first time the full phase stability of Ti-C-O and Al-C-O compounds using first-principles calculations, through simple, effcient and highly parallel random structure searching in conjunction with techniques based on complex network theory. This record contains the crystal structures used to generate our ternary convex hulls for these systems. We provide input files for the CASTEP density-functional theory code, crystallographic '.res' files of the relaxed structures, and CASTEP output files showing atomic positions and forces calculated during relaxation.

Latest version: v1
Publication date: Nov 30, 2021


Aluminum alloy compositions and properties extracted from a corpus of scientific manuscripts and US patents

DOI10.24435/materialscloud:tb-30

Olivia P. Pfeiffer, Haihao Liu, Luca Montanelli, Marat I. Latypov, Fatih G. Sen, Vishwanath Hegadekatte, Elsa A. Olivetti, Eric R. Homer

  • Researchers continue to explore and develop aluminum alloys with new compositions and improved performance characteristics. An understanding of the current design space can help accelerate the discovery of new alloys. We present two datasets: 1) chemical composition, and 2) mechanical properties for predominantly wrought aluminum alloys. The first dataset contains 14,884 entries on aluminum alloy compositions extracted from academic literature and US patents using text processing techniques, including 550 wrought aluminum alloys which are already registered with the Aluminum Association. The second dataset contains 1,278 entries on mechanical properties for aluminum alloys, where each entry is associated with a particular wrought series designation, extracted from tables in academic literature.

Latest version: v2
Publication date: Nov 29, 2021


3DMolNet: a generative network for molecular structures

DOI10.24435/materialscloud:g6-ft

Vitali Nesterov, Mario Wieser, Volker Roth

  • With the recent advances in machine learning for quantum chemistry, it is now possible to predict the chemical properties of compounds and to generate novel molecules. Existing generative models mostly use a string- or graph-based representation, but the precise three-dimensional coordinates of the atoms are usually not encoded. First attempts in this direction have been proposed, where autoregressive or GAN-based models generate atom coordinates. Those either lack a latent space in the autoregressive setting, such that a smooth exploration of the compound space is not possible, or cannot generalize to varying chemical compositions. We propose a new approach to efficiently generate molecular structures that are not restricted to a fixed size or composition. Our model is based on the variational autoencoder which learns a translation-, rotation-, and permutation-invariant low-dimensional representation of molecules. Our experiments yield a mean reconstruction error below 0.05 ...

Latest version: v1
Publication date: Nov 28, 2021


Graph theory-based structural analysis on density anomaly of silica glass

DOI10.24435/materialscloud:yv-e7

Aik Rui Tan, Shingo Urata, Masatsugu Yamada, Rafael Gómez-Bombarelli

  • Understanding the structure of glassy materials represents a tremendous challenge for both experiments and computations. Despite decades of scientific research, for instance, the structural origin of the density anomaly in silica glasses is still not well understood. Atomistic simulations based on molecular dynamics (MD) produce atomically resolved structure, but extracting insights about the role of disorder in the density anomaly is challenging. Here, we propose to quantify the topological differences between structural arrangements from MD trajectories using a graph-theoretical approach, such that structural differences in silica glasses that exhibit density anomaly can be captured. To balance the accuracy and speed of the MD simulations, we utilized force matching potentials to generate the silica glass structures. This approach involves casting all-atom glass configurations as networks, and subsequently applying a graph-similarity metric (D-measure). Calculated D-measure ...

Latest version: v1
Publication date: Nov 25, 2021


Assessment of approximate methods for anharmonic free energies

DOI10.24435/materialscloud:3j-c8

Venkat Kapil, Edgar Engel, Mariana Rossi, Michele Ceriotti

  • Quantitative evaluation of the thermodynamic properties of materials—most notably their stability, as measured by the free energy—must take into account the role of thermal and zero-point energy fluctuations. While these effects can easily be estimated within a harmonic approximation, corrections arising from the anharmonic nature of the interatomic potential are often crucial and require computationally costly path integral simulations to obtain results that are essentially exact for a given potential. Consequently, different approximate frameworks for computing affordable estimates of the anharmonic free energies have been developed over the years. Understanding which of the approximations involved are justified for a given system, and therefore choosing the most suitable method, is complicated by the lack of comparative benchmarks. To facilitate this choice we assess the accuracy and efficiency of some of the most commonly used approximate methods: the independent mode ...

Latest version: v2
Publication date: Nov 23, 2021


Inexpensive modeling of quantum dynamics using path integral generalized Langevin equation thermostats

DOI10.24435/materialscloud:td-wp

Venkat Kapil, David Wilkins, Jinggang Lan, Michele Ceriotti

  • The properties of molecules and materials containing light nuclei are affected by their quantum mechanical nature. Accurate modeling of these quantum nuclear effects requires computationally demanding path integral techniques. Considerable success has been achieved in reducing the cost of such simulations by using generalized Langevin dynamics to induce frequency-dependent fluctuations. Path integral generalized Langevin equation methods, however, have this far been limited to the study of static, thermodynamic properties due to the large perturbation to the system’s dynamics induced by the aggressive thermostatting. Here, we introduce a post-processing scheme, based on analytical estimates of the dynamical perturbation induced by the generalized Langevin dynamics, which makes it possible to recover meaningful time correlation properties from a thermostatted trajectory. We show that this approach yields spectroscopic observables for model and realistic systems that have an ...

Latest version: v2
Publication date: Nov 23, 2021


Bloch's theorem in orbital-density-dependent functionals: band structures from Koopmans spectral functionals

DOI10.24435/materialscloud:ee-vg

Riccardo De Gennaro, Nicola Colonna, Edward Linscott, Nicola Marzari

  • Koopmans-compliant functionals provide a novel orbital-density-dependent framework for an accurate evaluation of spectral properties; they are obtained by imposing a generalized piecewise-linearity condition on the total energy of the system with respect to the occupation of any orbital. In crystalline materials, due to the orbital-density-dependent nature of the functionals, minimization of the total energy to a ground state provides a set of minimizing variational orbitals that are localized, and thus break the periodicity of the underlying lattice. Despite this, we show that Bloch symmetry can be preserved and it is possible to describe the electronic states with a band-structure picture, thanks to the Wannier-like character of the variational orbitals. We also present a method to unfold and interpolate the electronic bands from supercell (Gamma-point) calculations, which enables us to calculate full band structures with Koopmans-compliant functionals. The results obtained for ...

Latest version: v1
Publication date: Nov 19, 2021


Finite-temperature materials modeling from the quantum nuclei to the hot electrons regime

DOI10.24435/materialscloud:vk-qd

Nataliya Lopanitsyna, Chiheb Ben Mahmoud, Michele Ceriotti

  • Atomistic simulations provide insights into structure-property relations on an atomic size and length scale that are complementary to the macroscopic observables that can be obtained from experiments. Quantitative predictions, however, are usually hindered by the need to strike a balance between the accuracy of the calculation of the interatomic potential and the modelling of realistic thermodynamic conditions. Machine-learning techniques make it possible to efficiently approximate the outcome of accurate electronic-structure calculations that can, therefore, be combined with extensive thermodynamic sampling. We take elemental nickel as a prototypical material, whose alloys have applications from cryogenic temperatures up to close to their melting point and use it to demonstrate how a combination of machine-learning models of electronic properties and statistical sampling methods makes it possible to compute accurate finite-temperature properties at an affordable cost. We ...

Latest version: v1
Publication date: Nov 16, 2021


Effects of perturbation order and basis set on alchemical predictions within 14 electron diatomic molecules series, detailed analysis of the various sources of errors

DOI10.24435/materialscloud:yg-r0

Giorgio Domenichini, Guido Falk von Rudorff, Otto Anatole von Lilienfeld

  • This Dataset contains Supplementary information to the article "Effects of perturbation order and basis set on alchemical predictions" by Giorgio Domenichini, Guido Falk von Rudorff and O. Anatole von Lilienfeld. Our numerical analysis of potential energy estimates, and resulting binding curves, is based on CCSD reference results, and is limited to all neutral diatomics with 14 electrons (AlH ... N2). From those data can be predicted binding energy, equilibrium distance, and vibrational frequencies of neighboring out-of-sample diatomics with near CCSD quality using perturbations up to 5th order. The data stored as Comma Separated Value files (.csv) contain all the predictions within the 14 electron diatomics series, those are referred to the sections IIIA-IIIE of the article. To every file corresponds one of the eight basis sets used. The data are stored using consistently atomic units: Bohrs for length, electrons for charge and Hartrees for energy. For a better visualization ...

Latest version: v1
Publication date: Nov 16, 2021


Oxygen vacancies in strontium titanate: a DFT+DMFT study

DOI10.24435/materialscloud:jf-zq

Jaime Souto-Casares, Nicola A. Spaldin, Claude Ederer

  • We address the long-standing question of the nature of oxygen vacancies in strontium titanate, using a combination of density functional theory and dynamical mean-field theory (DFT+DMFT) to investigate in particular the effect of vacancy-site correlations on the electronic properties. Our approach uses a minimal low-energy electronic subspace including the Ti-t2g orbitals plus an additional vacancy-centered Wannier function, and it provides an intuitive and physically transparent framework to study the effect of the local electron-electron interactions on the excess charge introduced by the oxygen vacancies. We estimate the strength of the screened interaction parameters using the constrained random phase approximation, and we find a sizable Hubbard U parameter for the vacancy orbital. Our main finding, which reconciles previous experimental and computational results, is that the ground state is either a state with double occupation of the localized defect state or a state with a ...

Latest version: v1
Publication date: Nov 09, 2021


Data for ferromagnetic resonance simulation in a microtube

DOI10.24435/materialscloud:gx-1d

Vladimir Fel'k, Sergey Komogortsev

  • Ferromagnetic resonance fields in a microtube with the various ratio of the inner and outer diameter of the tube β were studied using micromagnetic simulation. For β < 0.15 the resonance field agrees with the prediction of the Kittel equation for an infinite ferromagnetic cylinder for both parallel and perpendicular orientation of the applied field to its axis. For β > 0.15 the resonance field increases from the resonance field of the infinite cylinder and approaches the level of the film magnetized along the plane. This behavior was at odds both with the prediction that can be made using analytically calculated demagnetizing factor in ferromagnetic tube, and with the prediction that use the empirical dependence of the demagnetizing field on β, established from the magnetization curves. For β > 0.15 and transverse applied field a number of resonance peaks were observed.

Latest version: v2
Publication date: Nov 05, 2021


Exploring DFT+U parameter space with a Bayesian calibration assisted by Markov chain Monte Carlo sampling

DOI10.24435/materialscloud:16-d6

Pedram Tavadze, Reese Boucher, Guillermo Avendaño-Franco, Keenan X. Kocan, Sobhit Singh, Viviana Dovale-Farelo, Wilfredo Ibarra-Hernández, Matthew B Johnson, David S. Mebane, Aldo H Romero

  • Density-functional theory is widely used to predict the physical properties of materials. However, it usually fails for strongly correlated materials. A popular solution is to use the Hubbard corrections to treat strongly correlated electronic states. Unfortunately, the exact values of the Hubbard U and J parameters are initially unknown, and they can vary from one material to another. In this semi-empirical study, we explore the U and J parameter space of a group of iron-based compounds to simultaneously improve the prediction of physical properties (volume, magnetic moment, and bandgap). We used a Bayesian calibration assisted by Markov chain Monte Carlo sampling for three different exchange-correlation functionals (LDA, PBE, and PBEsol). We found that LDA requires the largest U correction. PBE has the smallest standard deviation and its U and J parameters are the most transferable to other iron-based compounds. Lastly, PBE predicts lattice parameters reasonably well without the Hubbard correction.

Latest version: v1
Publication date: Nov 03, 2021


Edge disorder in bottom-up zigzag graphene nanoribbons: implications for magnetism and quantum electronic transport

DOI10.24435/materialscloud:xf-r3

Michele Pizzochero, Gabriela Borin Barin, Kristiāns Čerņevičs, Shiyong Wang, Pascal Ruffieux, Roman Fasel, Oleg V. Yazyev

  • We unveil the nature of the structural disorder in bottom-up zigzag graphene nanoribbons along with its effect on the magnetism and electronic transport on the basis of scanning probe microscopies and first-principles calculations. We find that edge-missing m-xylene units emerging during the cyclodehydrogenation step of the on-surface synthesis are the most common point defects. These “bite” defects act as spin-1 paramagnetic centers, severely disrupt the conductance spectrum around the band extrema, and give rise to spin-polarized charge transport. We further show that the electronic conductance across graphene nanoribbons is more sensitive to “bite” defects forming at the zigzag edges than at the armchair ones. Our work establishes a comprehensive understanding of the low-energy electronic properties of disordered bottom-up graphene nanoribbons.

Latest version: v1
Publication date: Nov 03, 2021


Metallic carbon nanotube quantum dots with broken symmetries as a platform for tunable terahertz detection

DOI10.24435/materialscloud:vk-wp

Gilles Buchs, Magdalena Marganska, Jhon W. González, Kristjan Eimre, Carlo A. Pignedoli, Daniele Passerone, Andres Ayuela, Oliver Gröning, Dario Bercioux

  • In this record we provide data to support our recent findings related to carbon nanotube based quantum dots for tunable terahertz detection. Generating and detecting radiation in the technologically relevant range of the so-called terahertz gap (0.1–10 THz) is challenging because of a lack of efficient sources and detectors. Quantum dots in carbon nanotubes have shown great potential to build sensitive terahertz detectors, usually based on photon-assisted tunneling. A recently reported mechanism combining resonant quantum dot transitions and tunneling barrier asymmetries results in a narrow linewidth photocurrent response with a large signal-to-noise ratio under weak THz radiation. That device was sensitive to one frequency, corresponding to transitions between equidistant quantized states. In this work we show, using numerical simulations together with scanning tunneling spectroscopy studies of a defect-induced metallic zigzag single-walled carbon nanotube quantum dot, that ...

Latest version: v1
Publication date: Nov 02, 2021


Ab initio modeling framework for Majorana transport in 2D materials: towards topological quantum computing

DOI10.24435/materialscloud:8c-r3

Youseung Lee, Tarun Agarwal, Mathieu Luisier

  • We present an ab initio modeling framework to simulate Majorana transport in 2D semiconducting materials, paving the way for topological qubits based on 2D nanoribbons. By combining density-functional-theory and quantum transport calculations, we show that the signature of Majorana bound states (MBSs) can be found in 2D material systems as zero-energy modes with peaks in the local density-of-states. The influence of spin-orbit coupling and external magnetic fields on Majorana transport is studied for two relevant 2D materials, WSe2 and PbI2. To illustrate the capabilities of the proposed ab initio platform, a device structure capable of hosting MBSs is created from a PbI2 nanoribbon and carefully investigated. These results are compared to InSb nanowires and used to provide design guidelines for 2D topological qubits.

Latest version: v1
Publication date: Oct 31, 2021


Charge disproportionation and Hund's insulating behavior in a five-orbital Hubbard model applicable to d^4 perovskites

DOI10.24435/materialscloud:3s-b5

Maximilian E. Merkel, Claude Ederer

  • We explore the transition to a charge-disproportionated insulating phase in a five-orbital cubic tight-binding model applicable to transition-metal perovskites with a formal d^4 occupation of the transition-metal cation, such as ferrates or manganites. We use dynamical mean-field theory to obtain the phase diagram as a function of the average local Coulomb repulsion U and the Hund's coupling J. The main structure of the phase diagram follows from the zero band-width (atomic) limit and represents the competition between high-spin and low-spin homogeneous and an inhomogeneous charge-disproportionated state. This results in two distinct insulating phases: the standard homogeneous Mott insulator and the inhomogeneous charge-disproportionated insulator, recently also termed Hund's insulator. We characterize the unconventional nature of this Hund's insulating state. Our results are consistent with previous studies of two- and three-orbital models applicable to isolated t2g and eg ...

Latest version: v1
Publication date: Oct 29, 2021


High energy barriers for edge dislocation motion in body-centered cubic high entropy alloys

DOI10.24435/materialscloud:2y-yn

Recep Ekin Kubilay, Alireza Ghafarollahi, Francesco Maresca, W.A. Curtin

  • Recent theory proposes that edge dislocations in random body-centered cubic (BCC) high entropy alloys have high barriers for motion, conveying high strengths up to high temperatures. Here, the energy barriers for edge motion are computed for two model alloys, NbTaV and MoNbTaW as represented by interatomic potentials, using the Nudged Elastic Band method and compared to theoretical predictions. The average magnitude of the barriers and the average spacing of the barriers along the glide direction agree well with the analytical theory, with no adjustable parameters. The evolution of the barriers versus applied stress is modeled, and the mean strength is in reasonable agreement with the predicted zero-temperature strength. These findings validate the analytic theory. A reduced analytic model based on solute misfit volumes is then applied to Hf-Mo-Nb-Ta-Ti-Zr and Mo-Nb-Ta-Ti-V-W alloys, rationalizing the observed significant strength increases at room temperature and 1000 ∘C upon ...

Latest version: v1
Publication date: Oct 29, 2021


Analytical models of short-range order in FCC and BCC alloys

DOI10.24435/materialscloud:qa-ba

You Rao, William Curtin

  • A statistical-mechanics analysis is used to create analytic estimates for the short-range order (SRO) parameters in FCC and BCC solid solution alloys as a function of composition and temperature. As in the classic quasi-chemical method, the analysis assumes pair interactions among atoms at different distances and partitions the entire crystal into a set of identical independent clusters that are then treated like molecules in a gas. This enables analytic development of the probabilities that govern SRO. For binary and ternary alloys, increasingly complex clusters are considered that systematically extend the range of accuracy of the analytic model relative to reference Monte Carlo simulations. The results enable fast assessment of likely SRO using estimated inputs for atom-atom interaction energies. In this record we provide our analytical solution as well as the simulation data supporting our theoretical prediction of the short-range order parameter in both FCC and BCC alloys.

Latest version: v1
Publication date: Oct 29, 2021


Common workflows for computing material properties using different quantum engines

DOI10.24435/materialscloud:2a-yh

Sebastiaan P. Huber, Emanuele Bosoni, Marnik Bercx, Jens Bröder, Augustin Degomme, Vladimir Dikan, Kristjan Eimre, Espen Flage-Larsen, Alberto Garcia, Luigi Genovese, Dominik Gresch, Conrad Johnston, Guido Petretto, Samuel Poncé, Gian-Marco Rignanese, Christopher J. Sewell, Berend Smit, Vasily Tseplyaev, Martin Uhrin, Daniel Wortmann, Aliaksandr V. Yakutovich, Austin Zadoks, Pezhman Zarabadi-Poor, Bonan Zhu, Nicola Marzari, Giovanni Pizzi

  • The prediction of material properties through electronic-structure simulations based on density-functional theory has become routinely common, thanks, in part, to the steady increase in the number and robustness of available simulation packages. This plurality of codes and methods aiming to solve similar problems is both a boon and a burden. While providing great opportunities for cross-verification, these packages adopt different methods, algorithms, and paradigms, making it challenging to choose, master, and efficiently use any one for a given task. Leveraging recent advances in managing reproducible scientific workflows, we demonstrate how developing common interfaces for workflows that automatically compute material properties can tackle the challenge mentioned above, greatly simplifying interoperability and cross-verification. We introduce design rules for reproducible and reusable code-agnostic workflow interfaces to compute well-defined material properties, which we ...

Latest version: v2
Publication date: Oct 29, 2021


Impact of orientation misalignments on black phosphorus ultrascaled field-effect transistors

DOI10.24435/materialscloud:2v-ft

Cedric Klinkert, Sara Fiore, Jonathan Backmann, Youseung Lee, Mathieu Luisier

  • Advanced quantum transport approach from first-principle to shed light on the influence of orientation misalignments on the performance of BP-based field-effect transistors, for which the input files are reported. Both n-and p-type configurations are investigated for six alignment angles, in the ballistic limit of transport and in the presence of electron-phonon and charged impurity scattering.

Latest version: v1
Publication date: Oct 29, 2021


Mechanism and prediction of hydrogen embrittlement in fcc stainless steels and high entropy alloys

DOI10.24435/materialscloud:p2-4g

Xiao Zhou, Ali Tehranchi, W.A. Curtin

  • The urgent need for clean energy coupled with the exceptional promise of hydrogen (H) as a clean fuel is driving development of new metals resistant to hydrogen embrittlement. Experiments on new fcc high entropy alloys present a paradox: these alloys absorb more H than Ni or SS304 (austenitic 304 stainless steel) while being more resistant to embrittlement. Here, a new theory of embrittlement in fcc metals is presented based on the role of H in driving an intrinsic ductile-to-brittle transition at a crack tip. The theory quantitatively predicts the H concentration at which a transition to embrittlement occurs in good agreement with experiments for SS304, SS316L, CoCrNi, CoNiV, CoCrFeNi, and CoCrFeMnNi. The theory rationalizes why CoNiV is the alloy most resistant to embrittlement and why SS316L is more resistant than the high entropy alloys CoCrFeNi and CoCrFeMnNi, which opens a path for the computationally guided discovery of new embrittlement-resistant alloys.

Latest version: v1
Publication date: Oct 28, 2021


Large magnetic exchange coupling in rhombus-shaped nanographenes with zigzag periphery

DOI10.24435/materialscloud:vv-y6

Shantanu Mishra, Xuelin Yao, Qiang Chen, Kristjan Eimre, Oliver Gröning, Ricardo Ortiz, Marco Di Giovannantonio, Juan Carlos Sancho-García, Joaquín Fernández-Rossier, Carlo A. Pignedoli, Klaus Müllen, Pascal Ruffieux, Akimitsu Narita, Roman Fasel

  • In this record we provide data to support our recent findings for the magnetic properties of rhombus-shaped nanographenes. Nanographenes with zigzag edges are predicted to manifest non-trivial π-magnetism resulting from the interplay of concurrent electronic effects, such as hybridization of localized frontier states and Coulomb repulsion between valence electrons. This provides a chemically tunable platform to explore quantum magnetism at the nanoscale and opens avenues towards organic spintronics. The magnetic stability in nanographenes is thus far greatly limited by the weak magnetic exchange coupling, which remains below the room-temperature thermal energy. In our work, we report the synthesis of large rhombus-shaped nanographenes with zigzag peripheries on gold and copper surfaces. Single-molecule scanning probe measurements show an emergent magnetic spin singlet ground state with increasing nanographene size. The magnetic exchange coupling in the largest nanographene ...

Latest version: v1
Publication date: Oct 28, 2021


Intrinsic fracture behavior of Mg–Y alloys

DOI10.24435/materialscloud:nk-xk

Eleanor Mak, William Curtin

  • Pure magnesium (Mg) is an attractive metal for structural applications due to its low density, but also has low ductility and low fracture toughness. Dilute alloying of Mg with rare earth elements in small amounts improves the ductility, but the effects of alloying on fracture are not well-established. Here, the intrinsic fracture of a model Mg-3at%Y solid solution alloy is studied using a combination of anisotropic linear elastic fracture mechanics and atomistic simulations applied to a comprehensive set of crack configurations under mode I loading. The competition between brittle cleavage and ductile dislocation emission at the crack tip in Mg is improved slightly by alloying, because local fluctuations of the random solutes enable dislocation emission rather than cleavage fracture for a number of configurations where the differences in critical load for cleavage and emission are small. However, basalplane cleavage remains strongly preferred, as in pure Mg. The alloys do show ...

Latest version: v1
Publication date: Oct 28, 2021


Flat bands with fragile topology through superlattice engineering on single-layer graphene

DOI10.24435/materialscloud:bj-bh

Anastasiia Skurativska, Stepan S. Tsirkin, Fabian D Natterer, Titus Neupert, Mark H Fischer

  • 'Magic'-angle twisted bilayer graphene has received a lot of interest due to its flat bands with potentially non-trivial topology that lead to intricate correlated phases. A spectrum with flat bands, however, does not require a twist between multiple sheets of van der Waals materials, but rather can be realized with the application of an appropriate periodic potential. Here, we propose the imposition of a tailored periodic potential onto a single graphene layer through local perturbations that could be created via lithography or adatom manipulation, which also results in an energy spectrum featuring flat bands. Our first-principle calculations for an appropriate decoration of graphene with adatoms indeed show the presence of flat bands in the spectrum. Furthermore, we reveal the topological nature of the flat bands through a symmetry-indicator analysis. This non-trivial topology manifests itself in corner-localized states with a filling anomaly as we show using a tight-binding ...

Latest version: v1
Publication date: Oct 28, 2021


Nonlinear quantum magnetophononics in SrCu2(BO3)2

DOI10.24435/materialscloud:cp-6s

Flavio Giorgianni, Björn Wehinger, Stephan Allenspach, Nicola Colonna, Carlo Vicario, Pascal Puphal, Ekaterina Pomjakushina, Bruce Normand, Christian Rüegg

  • Harnessing the most advanced capabilities of quantum technologies will require the ability to control macroscopic quantum states of matter. Quantum magnetic materials provide a valuable platform for realizing highly entangled many-body quantum systems, and have been used to investigate phenomena ranging from quantum phase transitions (QPTs) to fractionalization, topological order and the entanglement structure of the quantum wavefunction. Although multiple studies have controlled their properties by static applied pressures or magnetic fields, dynamical control at the fundamental timescales of their magnetic interactions remains completely unexplored. However, major progress in the technology of ultrafast laser pulses has enabled the dynamical modification of electronic properties, and now we demonstrate the ultrafast control of quantum magnetism. This we achieve by a magnetophononic mechanism, the driving of coherent lattice displacements to produce a resonant excitation of the ...

Latest version: v1
Publication date: Oct 28, 2021


Theory of twin strengthening in fcc high entropy alloys

DOI10.24435/materialscloud:h4-0e

Recep Ekin Kubilay, W.A. Curtin

  • Twinning in fcc High Entropy Alloys (HEAs) has been implicated as a possible mechanism for hardening that enables enhanced ductility. Here, a theory for the twinning stress is developed analogous to recent theories for yield stress. Specifically, the stress to move a twin dislocation, i.e an fcc partial dislocation moving along a pre-existing twin boundary, through a random multicomponent alloy is determined. A reduced elasticity theory is then introduced in which atoms interact with the twin dislocation pressure field and the twin boundary. The theory is applied to NiCoCr using results from both interatomic potentials and elasticity theory. Results are also used to predict the increased stress for the motion of (i) a single partial dislocation leaving a trailing stacking fault and (ii) adjacent partial dislocations involved in twin nucleation. Increased strength is predicted for all processes involved in the nucleation and growth of fcc twins. Comparison to single-crystal ...

Latest version: v1
Publication date: Oct 28, 2021


Synthesis and characterization of [7]triangulene

DOI10.24435/materialscloud:av-cy

Shantanu Mishra, Kun Xu, Kristjan Eimre, Komber Hartmut, Ji Ma, Carlo A. Pignedoli, Roman Fasel, Xinliang Feng, Pascal Ruffieux

  • In this record we provide data to support our recent findings related to the fabrication of [7]triangulene. Triangulene and its π-extended homologues constitute non-Kekulé polyradical frameworks with high-spin ground states, and are anticipated to be key components of organic spintronic devices. In our publication we report a combined in-solution and on-surface synthesis of the hitherto largest triangulene homologue, [7]triangulene (C78H24), consisting of twenty-eight benzenoid rings fused in a triangular fashion. We employ low-temperature scanning tunneling microscopy to confirm the chemical structure of individual molecules adsorbed on a Cu(111) surface. While neutral [7]triangulene in the gas phase is predicted to have an open-shell septet ground state; our scanning tunneling spectroscopy measurements, in combination with density functional theory calculations, reveal chemisorption of [7]triangulene on Cu(111) together with considerable charge transfer, resulting in a ...

Latest version: v1
Publication date: Oct 28, 2021


First principles study of the effect of hydrogen in austenitic stainless steels and high entropy alloys

DOI10.24435/materialscloud:sw-20

Xiao Zhou, W.A. Curtin

  • Hydrogen (H) embrittlement in multicomponent austenitic alloys is a serious limitation to their application in many environments. Recent experiments show that the High-Entropy Alloy (HEA) CoCrFeMnNi absorbs more H than 304 Stainless Steel but is less prone to embrittlement while the HEA CoCrFeNi is not embrittled under comparable conditions. As a first step toward understanding H embrittlement, here a comprehensive first-principles study of H absorption, surface, and fracture energies in the presence of H is presented for 304 Stainless Steel, 316 Stainless Steel, CoCrFeNi, and CoCrFeMnNi. A collinear paramagnetic model of the magnetic state is used, which is likely more realistic than previous proposed magnetic states. All alloys have a statistical distribution of H absorption sites. Hence, at low concentrations, H is effectively trapped in the lattice making it more difficult for H to segregate to defects or interfaces. Agreement with experimental H solubilities across a range of ...

Latest version: v1
Publication date: Oct 28, 2021


Zeo-1: A computational data set of zeolite structures

DOI10.24435/materialscloud:cv-zd

Leonid Komissarov, Toon Verstraelen

  • Fast, empirical potentials are gaining increased popularity in the computational fields of materials science, physics and chemistry. With it, there is a rising demand for high-quality reference data for the training and validation of such models. In contrast to research that is mainly focused on small organic molecules, this work presents a data set of geometry-optimized bulk phase zeolite structures. Covering a majority of framework types from the Database of Zeolite Structures, this set includes over thirty thousand geometries. Calculated properties include system energies, nuclear gradients and stress tensors at each point, making the data suitable for model development, validation or referencing applications focused on periodic silica systems.

Latest version: v2
Publication date: Oct 27, 2021


On-surface synthesis of π-conjugated ladder-type polymers comprising nonbenzenoid moieties

DOI10.24435/materialscloud:a6-2z

José I. Urgel, Julian Bock, Marco Di Giovannantonio, Pascal Ruffieux, Carlo A. Pignedoli, Milan Kivala, Roman Fasel

  • In this record we provide data to support our recent findings related to the fabrication of π-conjugated ladder-type polymers comprising nonbenzenoid moieties. On-surface synthesis provides a powerful approach toward the atomically precise fabrication of π-conjugated ladder polymers (CLPs). In the manuscript we report the surface-assisted synthesis of nonbenzenoid CLPs from cyclopenta-annulated anthracene monomers on Au(111) under ultrahigh vacuum conditions. Successive thermal annealing steps reveal the dehalogenative homocoupling to yield an intermediate 1D polymer and the subsequent cyclodehydrogenation to form the fully conjugated ladder polymer. Notably, neighbouring monomers may fuse in two different ways, resulting in six- and five-membered rings, respectively. The structure and electronic properties of the reaction products have been investigated via low-temperature scanning tunneling microscopy and spectroscopy, complemented by density-functional theory calculations. Our ...

Latest version: v1
Publication date: Oct 26, 2021


On-surface activation of benzylic C–H bonds for the synthesis of pentagon-fused graphene nanoribbons

DOI10.24435/materialscloud:yc-k5

Xiushang Xu, Marco Di Giovannantonio, José I. Urgel, Carlo A. Pignedoli, Pascal Ruffieux, Klaus Müllen, Roman Fasel, Akimitsu Narita

  • In this record we provide data to support our recent findings related to the fabrication of pentagon-fused graphene nanoribbons. Graphene nanoribbons (GNRs) have potential for applications in electronic devices. A key issue, thereby, is the fine-tuning of their electronic characteristics, which can be achieved through subtle structural modifications. These are not limited to the conventional armchair, zigzag, and cove edges, but also possible through incorporation of non-hexagonal rings. On-surface synthesis enables the fabrication and visualization of GNRs with atomically precise chemical structures, but strategies for the incorporation of non-hexagonal rings have been underexplored. In the publication, we describe the on-surface synthesis of armchair-edged GNRs with incorporated five-membered rings through the C-H activation and cyclization of benzylic methyl groups. Ortho-Tolyl-substituted dibromobianthryl was employed as the precursor monomer, and visualization of the ...

Latest version: v1
Publication date: Oct 26, 2021


A ductility criterion for bcc high entropy alloys

DOI10.24435/materialscloud:s4-mm

Eleanor Mak, Binglun Yin, William Curtin

  • A current goal driving alloy development is the identification of alloy compositions for high temperature applications but with the additional requirement of sufficient ductility at ambient temperatures. Multicomponent, single-phase, polycrystalline High Entropy Alloys (HEAs) have recently emerged as a new class of metal alloys, and some refractory bcc HEAs composed mainly of Nb, V, Ta, Cr, Mo, and/or W show excellent strength retention up to very high temperatures but low ductility at room temperature (RT). Here, it is postulated that the macroscopic ductility in bcc elements and alloys is determined by the intrinsic competition between brittle cleavage and ductile dislocation emission mechanisms at an atomistically sharp crack. The stress intensities K_Ic for cleavage and K_Ie for emission are evaluated within Linear Elastic Fracture Mechanics and validated by atomistic simulations on model alloys. A RT ductility criterion based on K_Ie/K_Ic for critical crack orientations is ...

Latest version: v1
Publication date: Oct 26, 2021


Quantifying photoinduced polaronic distortions in inorganic lead halide perovskites nanocrystals

DOI10.24435/materialscloud:2p-e8

Oliviero Cannelli, Nicola Colonna, Michele Puppin, Thomas Rossi, Dominik Kinschel, Ludmila Leroy, Janina Löffler, Anne Marie March, Gilles Doumy, Andre Al Haddad, Ming-Feng Tu, Yoshiaki Kumagai, Donald Walko, Grigory Smolentsev, Franziska Krieg, Simon C. Boehme, Maksym V. Kovalenko, Majed Chergui, Giulia F. Mancini

  • The development of next generation perovskite-based optoelectronic devices relies critically on the understanding of the interaction between charge carriers and the polar lattice in out-of-equilibrium conditions. While it has become increasingly evident for CsPbBr3 perovskites that the Pb-Br framework flexibility plays a key role in their light-activated functionality, the corresponding local structural rearrangement has not yet been unambiguously identified. In this work, we demonstrate that the photoinduced lattice changes in the system are due to a specific polaronic distortion, associated with the activation of a longitudinal optical phonon mode at 18 meV by electron-phonon coupling, and we quantify the associated structural changes with atomic-level precision. Key to this achievement is the combination of time-resolved and temperature-dependent studies at Br K-edge and Pb L3-edge X-ray absorption with refined ab-initio simulations, which fully account for the screened ...

Latest version: v1
Publication date: Oct 25, 2021


High-throughput activity screening and sorting of single catalyst particles with a droplet microreactor using dielectrophoresis

DOI10.24435/materialscloud:em-r4

Anne-Eva Nieuwelink, Jeroen C. Vollenbroek, Roald M. Tiggelaar, Johan G. Bomer, Albert van den Berg, Mathieu Odijk, Bert M. Weckhuysen

  • This dataset, consisting of 29 videos, has been used for the publication 'High-Throughput Activity Screening and Sorting of Single Catalyst Particles with a Droplet Microreactor Using Dielectrophoresis': "A droplet microreactor has been developed for fluorescence activated sorting of catalyst particles using dielectrophoresis. Fluid Catalytic Cracking (FCC) particles stained with styrene derivatives are analyzed with the developed analytical platform and sorted based on catalytic activity. Highly active and low-to-moderately active catalyst particles are sorted out, using 4-fluorostyrene or 4-methoxystyrene as a probe respectively. The FCC particles are encapsulated in liquid droplets, where the fluorescent FCC particles activate the dielectrophoretic sorter, and are sorted within 200 ms."

Latest version: v1
Publication date: Oct 25, 2021


Elucidating the structure-dependent selectivity towards methane and ethanol of CuZn in the CO2 electroreduction using tailored Cu/ZnO precatalysts

DOI10.24435/materialscloud:3r-gn

Seyedeh Behnaz Varandili, Dragos Stoian, Jan Vavra, Kevin Rossi, James R Pankhurst, Yannick Guntern, Nuria Lopez, Raffaella Buonsanti

  • Understanding the catalyst compositional and structural features that control selectivity is of uttermost importance to target desired products in chemical reactions. In this joint experimental–computational work, we leverage tailored Cu/ZnO precatalysts as a material platform to identify the intrinsic features of methane-producing and ethanol-producing CuZn catalysts in the electrochemical CO2 reduction reaction (CO2RR). Specifically, we find that Cu@ZnO nanocrystals, where a central Cu domain is decorated with ZnO domains, and ZnO@Cu nanocrystals, where a central ZnO domain is decorated with Cu domains, evolve into Cu@CuZn core@shell catalysts that are selective for methane (∼52%) and ethanol (∼39%), respectively. Operando X-ray absorption spectroscopy and various microscopy methods evidence that a higher degree of surface alloying along with a higher concentration of metallic Zn improve the ethanol selectivity. Density functional theory explains that the combination of ...

Latest version: v1
Publication date: Oct 22, 2021


A new dataset of 175k stable and metastable materials calculated with the PBEsol and SCAN functionals

DOI10.24435/materialscloud:ka-br

Jonathan Schmidt, Hai-Chen Wang, Tiago F. T. Cerqueira, Silvana Botti, Miguel A. L. Marques

  • In the past decade we have witnessed the appearance of large databases of calculated material properties. These are most often obtained with the Perdew-Burke-Ernzerhof (PBE) functional of density-functional theory, a well established and reliable technique that is by now the standard in materials science. However, there have been recent theoretical developments that allow for an increased accuracy in the calculations. Here, we present a dataset of calculations for 175k solid-state materials obtained with two improved functionals: PBE for solids (that yields consistently better geometries than the PBE) and SCAN (probably the best all-around functional at the moment). Our results provide an accurate overview of the landscape of stable (and nearly stable) materials, and as such can be used for more reliable predictions of novel compounds. They can also be used for training machine learning models, or even for the comparison and benchmark of PBE, PBE for solids, and SCAN.

Latest version: v2
Publication date: Oct 20, 2021


Density functional Bogoliubov-de Gennes analysis of superconducting Nb and Nb(110) surfaces

DOI10.24435/materialscloud:9b-fv

Philipp Rüßmann, Stefan Blügel

  • Material-specific calculations based on density functional theory play a major role in understanding and designing the properties of quantum matter. In the field of topological quantum computing there is an intense search for material systems that have the ability to realize Majorana zero modes. The ability to combine the accurate electronic structure, that is accessible from density functional theory, with superconductivity can help gaining material-specific insights and may contribute to the understanding and realization of Majorana zero modes in solid state systems. In this work we report on our implementation of the Bogoliubov-de Gennes method into the JuKKR code [https://jukkr.fz-juelich.de], an implementation of the all-electron, full-potential Korringa-Kohn-Rostoker Green function method, which allows a material-specific description of inhomogeneous superconductors and heterostructures on the basis of density functional theory. We describe the formalism and report on ...

Latest version: v1
Publication date: Oct 15, 2021


Asymmetric elimination reaction on chiral metal surfaces

DOI10.24435/materialscloud:pm-8p

Samuel Stolz, Martina Danese, Marco Di Giovannantonio, José I. Urgel, Qiang Sun, Amogh Kinikar, Max Bommert, Shantanu Mishra, Harald Brune, Oliver Gröning, Daniele Passerone, Roland Widmer

  • The production of enantiopure materials and molecules is of uttermost relevance in research and industry in numerous contexts, ranging from non-linear optics to asymmetric synthesis. In the context of the latter, we have investigated dehalogenation, which is an essential reaction step for a broad class of chemical reactions. Specifically, dehalogenation of prochiral 5-bromo-7-methylbenz(a)anthracene (BMA) on prototypical, chiral, intermetallic PdGa{111} surfaces under ultrahigh vacuum conditions. Enantioselective halogen elimination is demonstrated by combining temperature-programmed x-ray photoelectron spectroscopy, scanning probe microscopy, and density functional theory. On the PdGa{111} surfaces, the difference in debromination temperatures for the two BMA surface enantiomers amounts up to unprecedented 46 K. The significant dependence of the dehalogenation temperature of the BMA surface enantiomers on the atomic termination of the PdGa{111} surfaces, implies that the ensemble ...

Latest version: v1
Publication date: Oct 11, 2021


Observation of fractional edge excitations in nanographene spin chains

DOI10.24435/materialscloud:e8-aq

Shantanu Mishra, Gonçalo Catarina, Fupeng Wu, Ricardo Ortiz, David Jacob, Kristjan Eimre, Ji Ma, Carlo A. Pignedoli, Xinliang Feng, Pascal Ruffieux, Joaquín Fernández-Rossier, Roman Fasel

  • Fractionalization is a phenomenon in which strong interactions in a quantum system drive the emergence of excitations with quantum numbers that are absent in the building blocks. Outstanding examples are excitations with charge e/3 in the fractional quantum Hall effect, solitons in one-dimensional conducting polymers and Majorana states in topological superconductors. Fractionalization is also predicted to manifest itself in low-dimensional quantum magnets, such as one-dimensional antiferromagnetic S = 1 chains. The fundamental features of this system are gapped excitations in the bulk and, remarkably, S = 1/2 edge states at the chain termini, leading to a four-fold degenerate ground state that reflects the underlying symmetry-protected topological order. This record contains data to support the result in a recent publication of ours where we use on-surface synthesis to fabricate one-dimensional spin chains that contain the S = 1 polycyclic aromatic hydrocarbon triangulene as the ...

Latest version: v1
Publication date: Oct 11, 2021


Optimizing accuracy and efficacy in data-driven materials discovery for the solar production of hydrogen

DOI10.24435/materialscloud:f4-wv

Yihuang Xiong, Quinn Campbell, Julian Fanghanel, Catherine Badding, Huaiyu Wang, Nicole Kirchner-Hall, Monica Theibault, Iurii Timrov, Jared Mondschein, Kriti Seth, Rebecca Katz, Andrés Molina Villarino, Betül Pamuk, Megan Penrod, Mohammed Khan, Tiffany Rivera, Nathan Smith, Xavier Quintana, Paul Orbe, Craig Fennie, Senorpe Asem-Hiablie, James Young, Todd Deutsch, Matteo Cococcioni, Venkatraman Gopalan, Héctor Abruña, Raymond Schaak, Ismaila Dabo

  • The production of hydrogen fuels, via water splitting, is of practical relevance for meeting global energy needs and mitigating the environmental consequences of fossil-fuel-based transportation. Water photoelectrolysis has been proposed as a viable approach for generating hydrogen, provided that stable and inexpensive photocatalysts with conversion efficiencies over 10% can be discovered, synthesized at scale, and successfully deployed (Pinaud et al., Energy Environ. Sci., 2013, 6, 1983). While a number of first-principles studies have focused on the data-driven discovery of photocatalysts, in the absence of systematic experimental validation, the success rate of these predictions may be limited. We address this problem by developing a screening procedure with co-validation between experiment and theory to expedite the synthesis, characterization, and testing of the computationally predicted, most desirable materials. Starting with 70150 compounds in the Materials Project ...

Latest version: v1
Publication date: Oct 08, 2021


How to extract adsorption energies, adsorbate-adsorbate interaction parameters, and saturation coverages from temperature programmed desorption experiments

DOI10.24435/materialscloud:b9-sq

Sudarshan Vijay, Henrik Kristoffersen, Yu Katayama, Yang Shao-Horn, Ib Chorkendorff, Brian Seger, Karen Chan

  • We present a scheme to extract the adsorption energy, adsorbate interaction parameter and the saturation coverage from temperature programmed desorption (TPD) experiments. We propose that the coverage dependent adsorption energy can be fit using a functional form including the configurational entropy and linear adsorbate-adsorbate interaction terms. As one example of this scheme, we analyze TPD of CO desorption on Au(211) and Au(310) surfaces. We determine that under atmospheric CO pressure, the steps of both facets adsorb between 0.4-0.9 ML coverage of CO*. We compare this result against energies obtained from five density functionals, RPBE, PBE, PBE-D3, RPBE-D3 and BEEF-vdW. We find that the energies and equilibrium coverages from RPBE-D3 and PBE are closest to the values determined from the TPD. This dataset contains all the DFT calculations run using AiiDA.

Latest version: v1
Publication date: Oct 08, 2021


Bayesian probabilistic assignment of chemical shifts in organic solids

DOI10.24435/materialscloud:vp-ft

Manuel Cordova, Martins Balodis, Bruno Simões de Almeida, Michele Ceriotti, Lyndon Emsley

  • A pre-requisite for NMR studies of organic materials is assigning each experimental chemical shift to a set of geometrically equivalent nuclei. Obtaining the assignment experimentally can be challenging and typically requires time-consuming multi-dimensional correlation experiments. An alternative solution for determining the assignment involves statistical analysis of experimental chemical shift databases, but no such database exists for molecular solids. Here, by combining the Cambridge structural database with a machine learning model of chemical shifts, we construct a statistical basis for probabilistic chemical shift assignment of organic crystals by calculating shifts for over 200,000 compounds, enabling the probabilistic assignment of organic crystals directly from their two-dimensional chemical structure. The approach is demonstrated with the 13C and 1H assignment of eleven molecular solids with experimental shifts, and benchmarked on 100 crystals using predicted shifts. ...

Latest version: v1
Publication date: Oct 06, 2021


Property map collective variable as a useful tool for force field correction

DOI10.24435/materialscloud:bx-gb

Dalibor Trapl, Martin Krupička, Vladimir Višňovský, Jana Hozzová, Jaroslav Oľha, Aleš Křenek, Vojtěch Spiwok

  • Molecular mechanics potentials for small molecules suffer inaccuracies. To apply corrections we used a concept called property map to calculate corrections. It was calculated as a sum of [correction_i exp(-lambda D(x, x_i))] divided by the sum of [exp(-lambda D(x, x_i))], where correction_i is the difference between the accurate and inaccurate potential for i-th landmark structure x_i, lambda is a chosen prefactor, D is a distance (e.g. RMSD or MSD) and x are atomic coordinates. The concept was tested on alanine dipeptide (all combinations of 7 force fields, one used as a model of accurate and one as inaccurate). Next it was applied on an anticancer drug Imatinib (General AMBER Force Field corrected to DFT). Simulations were carried out in Gromacs 2016.4. DFTB/MM simulation was carried out in CP2K 7.1. Correction was Implemented using Plumed 2.4. DFT energies were calculated by ORCA 4.0 at the BP86/def2-TZVP level of theory.

Latest version: v2
Publication date: Oct 05, 2021


Unified mechanistic understanding of CO2 reduction to CO on transition metal and single atom catalysts

DOI10.24435/materialscloud:ws-7t

Sudarshan Vijay, Wen Ju, Sven Brückner, Sze-Chun Tsang, Peter Strasser, Karen Chan

  • CO is the simplest product from CO2 electroreduction (CO2R), but the identity and nature of its rate limiting step remains controversial. Here we investigate the activity of both transition metals (TMs) and metal-nitrogen doped carbon catalysts (MNCs), and a present unified mechanistic picture of CO2R for both these classes of catalysts. By consideration of the electronic structure through a Newns-Andersen model, we find that on MNCs, like TMs, electron transfer to CO2 is facile, such that CO2 (g) adsorption is driven by adsorbate dipole-field interactions. Using density functional theory with explicit consideration of the interfacial field, we find CO2 * adsorption to generally be limiting on TMs, while MNCs can be limited by either CO2* adsorption or by the proton-electron transfer reaction to form COOH*. We evaluate these computed mechanisms against pH-dependent experimental activity measurements on CO2R to CO activity for Au, FeNC, and NiNC. We present a unified activity ...

Latest version: v1
Publication date: Sep 28, 2021


A dataset for beta-glycine with Wannier centers

DOI10.24435/materialscloud:jn-44

Maarten Cools-Ceuppens, Joni Dambre, Toon Verstraelen

  • The beta-glycine dataset is created with the purpose of validating the electron machine learning potential (eMLP) on crystalline beta glycine. It contains 25,676 configurations with normal mode perturbations for the nuclei and unit cell and electric field perturbations. Energies, forces and Wannier centers are computed using density functional theory (DFT) with the PBE functional and a Plane-Wave basis set in the ab-initio quantum chemistry code QuantumESPRESSO.

Latest version: v1
Publication date: Sep 27, 2021


eQM7: a dataset for small molecules with Foster-Boys centers

DOI10.24435/materialscloud:66-9j

Maarten Cools-Ceuppens, Joni Dambre, Toon Verstraelen

  • The electron QM7 (eQM7) dataset is created with the purpose of training and validating polarizable (machine learning) force fields on non-equilibrium configurations of small molecules. It contains 6868 molecules with hydrogen, carbon, nitrogen and oxygen. For each molecule, 500 perturbations are constructed using normal mode sampling, torsion sampling, dimer sampling and homogeneous electric fields. Energies, forces and Foster-Boys centers are computed using density functional theory (DFT) with the PBE0 functional, Aug-cc-pVTZ basis set in the ab-initio quantum chemistry code Psi4.

Latest version: v1
Publication date: Sep 27, 2021


Properties of α-brass nanoparticles. 1. Neural network potential energy surface

DOI10.24435/materialscloud:94-aq

Jan Weinreich, Martín Leandro Paleico, Anton Roemer

  • **Data for Properties of α-Brass Nanoparticles. 1. Neural Network Potential Energy Surface** Jan Weinreich, Anton Römer, Martín Leandro Paleico, and Jörg Behler 53 841 reference structures of alpha brass (less 40 % Zn) with following split - 4009 brass clusters - 8492 molten brass bulk structures - 8964 copper slabs, and 16 878 brass slabs - 5377 copper bulk structures - 10 121 brass bulk structures have been included. 53 841 total energies and 8 903 340 force components. The ranges of values for the energies and force components to be fitted have a width of about 2 eV/atom and 15 eV/Å, respectively. However, some structures may have slightly higher Zn content as discussed in Fig 3 (https://arxiv.org/abs/2001.10906) The archive contains an easily usable npz file as well as the original input.data file used to fit the potential energy surface. Additionally a Jupyter notebook describes in great detail how the data was converted to the npz format and how to read the data ...

Latest version: v1
Publication date: Sep 26, 2021


Improving the silicon interactions of GFN-xTB

DOI10.24435/materialscloud:14-4m

Leonid Komissarov, Toon Verstraelen

  • This record addresses inaccuracies in the widely-used GFN-xTB model when it comes to the description of organosilicon compounds. Here, an ab initio reference data set of 10000 compounds is provided alongside files needed to execute a parameter fitting scheme that improves geometries, nuclear gradients and energies predicted by the GFN-xTB Hamiltonian.

Latest version: v1
Publication date: Sep 21, 2021


On-surface synthesis and characterization of super-nonazethrene

DOI10.24435/materialscloud:j7-51

Elia Turco, Shantanu Mishra, Jason Melidonie, Kristjan Eimre, Sebastian Obermann, Carlo A. Pignedoli, Roman Fasel, Xinliang Feng, Pascal Ruffieux

  • This record contains data to support the findings discussed in our recent work on the synthesis and characterization of super-nonazethrene. Beginning with the early work of Clar et al. in 1955, zethrenes and their laterally-extended homologues, super-zethrenes, have been intensively studied in the solution phase, and are widely investigated as optical and charge transport materials. Super-zethrenes are also considered to exhibit an open-shell ground state. Zethrenes may thus serve as model compounds to investigate nanoscale π-magnetism. However, their synthesis is extremely challenging due to their high reactivity. In the work we report here a combined in-solution and on-surface synthesis of the hitherto largest zethrene homologue – super-nonazethrene – on Au(111). Using single-molecule scanning tunneling microscopy and spectroscopy, we show that super-nonazethrene exhibits an open-shell singlet ground state featuring a large spin polarization-driven electronic gap of 1 eV. We ...

Latest version: v1
Publication date: Sep 20, 2021


Machine learning of superconducting critical temperature from Eliashberg theory

DOI10.24435/materialscloud:68-6p

Stephen Xie, Yundi Quan, Ajinkya Hire, Boning Deng, Jonathan DeStefano, Ian Salinas, Urja Shah, Laura Fanfarillo, Jinhyuk Lim, Jungsoo Kim, Gregory Stewart, James Hamlin, Peter Hirschfeld, Richard Hennig

  • The Eliashberg theory of superconductivity accounts for the fundamental physics of conventional electron-phonon superconductors, including the retardation of the interaction and the effect of the Coulomb pseudopotential, to predict the critical temperature Tc and other properties. McMillan, Allen, and Dynes derived approximate closed-form expressions for the critical temperature predicted by this theory, which depends essentially on the electron-phonon spectral function α²F(ω), using α²F for low-Tc superconductors. Here we show that modern machine learning techniques can substantially improve these formulae, accounting for more general shapes of the α²F function. Using symbolic regression and the sure independence screening and sparsifying operator (SISSO) framework, together with a database of artificially generated α²F functions, ranging from multimodal Einstein-like models to calculated spectra of polyhydrides, as well as numerical solutions of the Eliashberg equations, we ...

Latest version: v1
Publication date: Sep 18, 2021


Sensitivity benchmarks of structural representations for atomic-scale machine learning

DOI10.24435/materialscloud:7z-g6

Sergey Pozdnyakov, Michele Ceriotti

  • This dataset contains three sets of CH4 geometries that are distorted along special directions, to reveal the sensitivity to atomic displacements of structural descriptors used in machine-learning applications. The structures are stored in a format that can be visualized on http://chemiscope.org, and contain also DFT-computed energies, as well as the sensitivity analysis of four different kinds of features.

Latest version: v1
Publication date: Sep 17, 2021


Deep learning the slow modes for rare events sampling

DOI10.24435/materialscloud:3g-9x

Luigi Bonati, GiovanniMaria Piccini, Michele Parrinello

  • The development of enhanced sampling methods has greatly extended the scope of atomistic simulations, allowing long-time phenomena to be studied with accessible computational resources. Many such methods rely on the identification of an appropriate set of collective variables. These are meant to describe the system's modes that most slowly approach equilibrium. Once identified, the equilibration of these modes is accelerated by the enhanced sampling method of choice. An attractive way of determining the collective variables is to relate them to the eigenfunctions and eigenvalues of the transfer operator. Unfortunately, this requires knowing the long-term dynamics of the system beforehand, which is generally not available. However, we have recently shown that it is indeed possible to determine efficient collective variables starting from biased simulations. In this paper, we bring the power of machine learning and the efficiency of the recently developed on-the-fly probability ...

Latest version: v1
Publication date: Sep 16, 2021


Magnetic and electronic properties at the γ-Al2O3/SrTiO3 interface

DOI10.24435/materialscloud:xx-et

Jose Mardegan, Dennis Christensen, Yunzhong Chen, Sergii Parchenko, Sridhar Avula, Nazaret Ortiz-Hernandez, Martin Decker, Cinthia Piamonteze, Nini Pryds, Urs Staub

  • The magnetic and electronic nature of the γ-Al2O3/SrTiO3 spinel/perovskite interface is explored by means of x-ray absorption spectroscopy. Polarized x-ray techniques combined with atomic multiplet calculations reveal localized magnetic moments assigned to Ti3+ at the interface with equivalent size for in- and out-of-plane magnetic field directions. Although magnetic fingerprints are revealed, the Ti3+ magnetism can be explained by a paramagnetic response at low temperature under applied magnetic fields. Modeling the x-ray linear dichroism results in a Delta0 ∼ 1.9 eV splitting between the t2g and eg states for the Ti4+ 3d0 orbitals. In addition these results indicate that the lowest energy states have the out-of-plane dxz/dyz symmetry. The isotropic magnetic moment behavior and the lowest energy dxz/dyz states are in contrast to the observations for the two-dimensional electron gas at the perovskite/perovskite interface of LaAlO3/SrTiO3 that exhibits an anisotropic magnetic dxy ground state.

Latest version: v1
Publication date: Sep 13, 2021


Gas transport across carbon nitride nanopores: a comparison of van der Waals functionals against the random-phase approximation

DOI10.24435/materialscloud:pn-w9

Mohammad Tohidi Vahdat, Davide Campi, Nicola Colonna, Nicola Marzari, Kumar Agrawal Varoon

  • C2N is an ordered two-dimensional carbon nitride with a high density (1.7 × 10^14 cm−2) of 3.1 Å-sized nanopores, making it promising for high-flux gas sieving for energy-efficient He and H2 purification. Herein, we discuss the accurate calculation of potential energy surfaces for He, H2, N2, and CO2 across C2N nanopores, to characterize the gas-sieving potential of C2N. We compare the potential energy surface derived from density-functional theory calculations using five commonly used van der Waals (vdW) approximations. While all five functionals point that the C2N nanopore yields He/N2 and H2/N2 selectivities over 1000, adsorption energies and energy barriers vary remarkably depending on the approximation chosen. To make progress, we compare the calculations against the results from the adiabatic connection fluctuation dissipation theory, with random-phase approximation, known to be accurate in capturing vdW interactions. The comparison indicates that the interaction energy is ...

Latest version: v1
Publication date: Sep 07, 2021


Design rules for interconnects based on graphene nanoribbon junctions

DOI10.24435/materialscloud:zb-ed

Kristiāns Čerņevičs, Oleg V. Yazyev

  • Graphene nanoribbons (GNRs) produced by means of bottom-up chemical self-assembly are considered promising candidates for the next-generation nanoelectronic devices. We address the electronic transport properties of angled two-terminal GNR junctions, which are inevitable in the interconnects in graphene-based integrated circuits. We construct a library of over 400000 distinct configurations of 60° and 120° junctions connecting armchair GNRs of different widths. Numerical calculations combining the tight-binding approximation and the Green’s function formalism allow identifying numerous junctions with conductance close to the limit defined by the GNR leads. Further analysis reveals underlying structure-property relationships with crucial roles played by the bipartite symmetry of graphene lattice and the presence of resonant states localized at the junction. In particular, we discover and explain the phenomenon of binary conductance in 120° junctions connecting metallic GNR leads ...

Latest version: v1
Publication date: Sep 01, 2021


Interface polarization in heterovalent core/shell nanocrystals

DOI10.24435/materialscloud:xk-xk

Byeong Guk Jeong, Jun Hyuk Chang, Donghyo Hahm, Seunghyun Rhee, Myeongjin Park, Sooho Lee, Youngdu Kim, Doyoon Shin, Jeong Woo Park, Changhee Lee, Doh C. Lee, Kyoungwon Park, Euyheon Hwang, Wan Ki Bae

  • The potential profile and the energy level offset of core/shell heterostructured nanocrystals (h-NCs) determine the photophysical properties and the charge transport characteristics of h-NC solids. However, limited material choices for heavy metal-free III-V/II-VI h-NCs pose challenges in comprehensive control of the potential profile. Herein, we present an approach to such control by steering dipole densities at the interface of III-V/II-VI h-NCs. The controllable heterovalency at the interface is responsible for interfacial dipole densities that result in the vacuum-level shift, providing an additional knob for the control of optical and electrical characteristics of h-NCs. The synthesis of h-NCs with atomic precision allows us to correlate interfacial dipole moments with the nanocrystals’ photochemical stability and optoelectronic performance. The description was referred to the abstract of the original paper. All numerical data of the main figures in the articles are included ...

Latest version: v1
Publication date: Aug 31, 2021


Ultrafast electron localization in the EuNi2(Si0.21Ge0.79)2 correlated metal

DOI10.24435/materialscloud:5f-y0

Jose Mardegan, Serhane Zerdane, Giulia Mancini, Vincent Esposito, Jeremy Rouxel, Roman Mankowsky, Cristian Svetina, Namrata Gurung, Sergii Parchenko, Michael Porer, Bulat Burganov, Yunpei Deng, Paul Beaud, Gerhard Ingold, Bill Pedrini, Christopher Arrell, Christian Erny, Andreas Dax, Henrik Lemke, Martin Decker, Nazaret Ortiz, Chris Milne, Grigory Smolentsev, Laura Maurel, Steven Johnson, Akihiro Mitsuda, Hirofumi Wada, Yuichi Yokoyama, Hiroki Wadati, Urs Staub

  • Ultrafast electron delocalization induced by a femtosecond laser pulse is a well-known process in which electrons are ejected from the ions within the laser pulse duration. However, very little is known about the speed of electron localization out of an electron gas in correlated metals, i.e., the capture of an electron by an ion. Here, we demonstrate by means of pump-probe x-ray techniques across the Eu L3 absorption edge that an electron localization process in the EuNi2(Si0.21Ge0.79)2 intermetallic material occurs within a few hundred femtoseconds after the optical excitation. Spectroscopy and diffraction data collected simultaneously at low temperature and for various laser fluences show that the localization dynamics process is much faster than the thermal expansion of the unit cell along the c direction which occurs within picoseconds. Nevertheless, this latter process is still much slower than pure electronic effects, such as screening, and the subpicosecond timescale ...

Latest version: v1
Publication date: Aug 31, 2021


Facet-dependent stability of near-surface oxygen vacancies and excess charge localization at CeO2 surfaces

DOI10.24435/materialscloud:ax-hy

Patricia Pérez-Bailac, Pablo G. Lustemberg, M. Verónica Ganduglia-Pirovano

  • To study the dependence of the relative stability of surface (VA) and subsurface (VB) oxygen vacancies with the crystal facet of CeO2, the reduced (100), (110) and (111) surfaces, with two different concentrations of vacancies, were investigated by means of density functional theory (DFT+U) calculations. The results show that the trend in the near-surface vacancy formation energies for comparable vacancy spacings, i.e. (110) < (100) < (111), does not follow that in the surface stability of the facets, i.e. (111) < (110) < (100). The results also revealed that the preference of vacancies for surface or subsurface sites, as well as the preferred location of the associated Ce3+ polarons, are facet and concentration dependent. At the higher vacancy concentration, the VA is more stable than the VB at the (110) facet whereas at the (111), it is the other way around, and at the (100) facet, both the VA and the VB have similar stability. The stability of the VA vacancies, compared to that ...

Latest version: v1
Publication date: Aug 31, 2021


Ab initio electron-phonon interactions in correlated electron systems

DOI10.24435/materialscloud:jt-32

Jin-Jian Zhou, Jinsoo Park, Iurii Timrov, Andrea Floris, Matteo Cococcioni, Nicola Marzari, Marco Bernardi

  • Electron-phonon (e-ph) interactions are pervasive in condensed matter, governing phenomena such as transport, superconductivity, charge-density waves, polarons, and metal-insulator transitions. First-principles approaches enable accurate calculations of e-ph interactions in a wide range of solids. However, they remain an open challenge in correlated electron systems (CES), where density functional theory often fails to describe the ground state. Therefore reliable e-ph calculations remain out of reach for many transition metal oxides, high-temperature superconductors, Mott insulators, planetary materials, and multiferroics. Here we show first-principles calculations of e-ph interactions in CES, using the framework of Hubbard-corrected density functional theory (DFT+U) and its linear response extension (DFPT+U), which can describe the electronic structure and lattice dynamics of many CES. We showcase the accuracy of this approach for a prototypical Mott system, CoO, carrying out a ...

Latest version: v1
Publication date: Aug 30, 2021


Vertex function compliant with the Ward identity for quasiparticle self-consistent calculations beyond GW

DOI10.24435/materialscloud:hb-v3

Alexey Tal, Wei Chen, Alfredo Pasquarello

  • We extend the quasiparticle self-consistent approach beyond the GW approximation by using a range-separated vertex function. The developed approach yields band gaps, dielectric constants, and band positions with an accuracy similar to highest-level electronic-structure calculations without exceeding the cost of regular quasiparticle self-consistent GW. We introduce an exchange-correlation kernel that accounts for the vertex over the full spatial range. In the long range it complies with the Ward identity, while it is approximated through the adiabatic local density functional in the short range. In this approach, the renormalization factor is balanced and the higher-order diagrams are effectively taken into account.

Latest version: v1
Publication date: Aug 27, 2021


First-principles and experimental characterization of the electronic and optical properties of CaS and CaO

DOI10.24435/materialscloud:d4-mn

Samuel Poncé, Bruno Bertrand, Philip F. Smet, Dirk Poelman, Masayoshi Mikami, Xavier Gonze

  • Doped alkaline-earth chalcogenides are interesting photoluminescent materials for opto-electronic applications. It is crucial to have an extended knowledge about the undoped bulk CaS and CaO since all the excited state properties of the doped material heavily depend on it. In this work we investigate the structural parameters, electronic band structures, macroscopic dielectric constants and absorption spectra for CaS and CaO compounds. Their quasi-particle band structure in the GW approximation yields a value of 4.28 eV and 6.02 eV for the indirect theoretical particle gap of CaS and CaO, respectively. The imaginary part of the macroscopic dielectric function e(omega) is computed including excitonic effects through the Bethe–Salpeter equation. The onset of absorption is within 0.1 eV of the experimental one and the calculated spectrum shows a qualitative agreement with experiment. Our computed exciton binding energies are 0.27 eV and 0.40 eV for CaS and CaO, respectively.

Latest version: v1
Publication date: Aug 20, 2021


Temperature dependence of electronic eigenenergies in the adiabatic harmonic approximation

DOI10.24435/materialscloud:1n-2d

Samuel Poncé, Gabriel Antonius, Yannick Gillet, Paul Boulanger, Jonathan Laflamme Janssen, Andrea Marini, Michel Côté, Xavier Gonze

  • The renormalization of electronic eigenenergies due to electron-phonon interactions (temperature dependence and zero-point motion effect) is important in many materials. We address it in the adiabatic harmonic approximation, based on first principles (e.g., density-functional theory), from different points of view: directly from atomic position fluctuations or, alternatively, from Janak’s theorem generalized to the case where the Helmholtz free energy, including the vibrational entropy, is used. We prove their equivalence, based on the usual form of Janak’s theorem and on the dynamical equation. We then also place the Allen-Heine-Cardona (AHC) theory of the renormalization in a first-principles context. The AHC theory relies on the rigid-ion approximation, and naturally leads to a self-energy (Fan) contribution and a Debye-Waller contribution. Such a splitting can also be done for the complete harmonic adiabatic expression, in which the rigid-ion approximation is not required. A ...

Latest version: v1
Publication date: Aug 20, 2021


Temperature dependence of the electronic structure of semiconductors and insulators

DOI10.24435/materialscloud:cj-c4

Samuel Poncé, Yannick Gillet, Jonathan Laflamme Janssen, Andrea Marini, Matthieu Verstraete, Xavier Gonze

  • The renormalization of electronic eigenenergies due to electron-phonon coupling (temperature dependence and zero-point motion effect) is sizable in many materials with light atoms. This effect, often neglected in ab initio calculations, can be computed using the perturbation-based Allen-Heine-Cardona theory in the adiabatic or non-adiabatic harmonic approximation. After a short description of the recent progresses in this field and a brief overview of the theory, we focus on the issue of phonon wavevector sampling convergence, until now poorly understood. Indeed, the renormalization is obtained numerically through a slowly converging q-point integration. For non-zero Born effective charges, we show that a divergence appears in the electron-phonon matrix elements at q → Γ, leading to a divergence of the adiabatic renormalization at band extrema. This problem is exacerbated by the slow convergence of Born effective charges with electronic wavevector sampling, which leaves residual ...

Latest version: v1
Publication date: Aug 20, 2021


Understanding thermal quenching of photoluminescence in oxynitride phosphors from first principles

DOI10.24435/materialscloud:sn-np

Samuel Poncé, Yongchao Jia, Matteo Giantomassi, Masayoshi Mikami, Xavier Gonze

  • Understanding the physical mechanisms behind thermal effects in phosphors is crucial for white light-emitting device (WLEDs) applications, as thermal quenching of their photoluminescence might render them useless. We analyze from first-principles, before and after absorption/emission of light, two chemically close Eu-doped Ba₃Si₆O₁₂N₂ and Ba₃Si₆O₉N₄ crystals for WLEDs. The first one has an almost constant emission intensity with increasing temperature whereas the other one does not. Our results, in which the Eu-5d levels are obtained inside the band gap thanks to the removal of an electron from the 4f⁷ shell, and the atomic neighborhood properly relaxed in the excited state, attributes the above-mentioned experimental difference to an autoionization model of the thermal quenching, based on the energy difference between Eu 5d and the conduction band minimum. Our depleted-shifted 4f method can identify luminescent centers and therefore allows for effective crystal site engineering ...

Latest version: v1
Publication date: Aug 20, 2021


Origin of low carrier mobilities in halide perovskites

DOI10.24435/materialscloud:t0-kw

Samuel Poncé, Martin Schlipf, Feliciano Giustino

  • Halide perovskites constitute a new class of semiconductors that hold promise for low-cost solar cells and optoelectronics. One key property of these materials is the electron mobility, which determines the average electron speed due to a driving electric field. Here we elucidate the atomic-scale mechanisms and theoretical limits of carrier mobilities in halide perovskites by performing a comparative analysis of the archetypal compound CH₃NH₃PbI₃, its inorganic counterpart CsPbI₃, and a classic semiconductor for light-emitting diodes, wurtzite GaN, using cutting-edge many-body ab initio calculations. We demonstrate that low-energy longitudinal-optical phonons associated with fluctuations of the Pb−I bonds ultimately limit the mobility to 80 cm² /(V s) at room temperature. By extending our analysis to a broad class of compounds, we identify a universal scaling law for the carrier mobility in halide perovskites, and we establish the design principles to realize high-mobility materials.

Latest version: v1
Publication date: Aug 19, 2021


Atomic structures of 100nm x 100nm large oxide-, nitride-, sulfide-, and phosphide-derived copper surfaces

DOI10.24435/materialscloud:3s-7w

Joseph Gauthier, Joakim Halldin Stenlid, Frank Abild-Pedersen, Martin Head-Gordon, Alexis T. Bell

  • Cif files of relaxed "derived" copper surfaces from Cu2O, Cu2S, Cu3N, and Cu3P using EMT and published in J Gauthier, JH Stenlid, F Abild-Pedersen, M Head-Gordon, AT Bell, ACS Energy Letters, "The role of roughening to enhance selectivity to C2+ products during CO2 electroreduction on copper" (2021). These structures were used to evaluate the effect of roughening on catalytic selectivity of copper in electrochemcial CO2 reduction into valuable products such as fuels and commodity chemicals.

Latest version: v1
Publication date: Aug 12, 2021


Hidden spontaneous polarisation in the chalcohalide photovoltaic Sn2SbS2I3

DOI10.24435/materialscloud:ge-qt

Seán R. Kavanagh, Christopher N. Savory, David O. Scanlon, Aron Walsh

  • Enormous research efforts are currently devoted to the discovery of ‘perovskite-inspired materials’, aiming to replicate the astonishing optoelectronic performance of lead-halide perovskites (LHPs). Recently, chalco halides of group IV/V elements have attracted attention due to the stability provided by stronger metal-chalcogen bonds, alongside compositional flexibility and ns2 cations — a performance-defining feature of LHPs. Following the experimental report of stable, solution-grown tin-antimony sulfoiodide (Sn2SbS2I3) solar cells, with power conversion efficiencies above 4%, we comprehensively characterise the structural and electronic properties of this emerging material. We find that the experimentally-reported centrosymmetric Cmcm crystal structure represents an average over multiple polar Cmc2_1 configurations. This dynamic crystal structure and ferroelectric behaviour could benefit photovoltaic performance. Using state-of-the-art ab initio methods, we assess the ...

Latest version: v1
Publication date: Aug 11, 2021


Pushing the limits of the donor-acceptor copolymer strategy for intramolecular singlet fission

DOI10.24435/materialscloud:mt-ey

Maria Fumanal, Clémence Corminboeuf

  • Donor–acceptor (D–A) copolymers have shown great potential for intramolecular singlet fission (iSF). Nonetheless, very few design principles exist for optimizing these systems for iSF, with very little knowledge about how to engineer them for this purpose. In recent work, a fundamental trade-off between the main electronic ingredients required for iSF capable D–A coplanar copolymers was revealed. Still, further investigations are needed to understand these limitations and learn how to bypass them. In this work, we propose to induce torsion as an effective way to circumvent the limits of the coplanar approach. We disclose the potential of noncoplanar copolymers with inherently low triplet energies that encompass all the characteristics required for iSF beyond the limiting values associated with fully coplanar systems. Our findings shed some light on the electronic structure aspects of D–A copolymers for iSF and offer a new avenue for the rational design of novel promising candidates.

Latest version: v1
Publication date: Aug 11, 2021


Data-driven simulation and characterisation of gold nanoparticles melting

DOI10.24435/materialscloud:s0-24

Claudio Zeni, Kevin Rossi, Theodore Pavloudis, Joseph Kioseoglou, Stefano de Gironcoli, Richard E. Palmer, Francesca Baletto

  • We develop efficient, accurate, transferable, and interpretable machine learning force fields for Au nanoparticles, based on data gathered from Density Functional Theory calculations. We then use them to investigate the thermodynamic stability of Au nanoparticles of different sizes (1 to 6 nm), containing up to 6266 atoms, with respect to a solid-liquid phase change through molecular dynamics simulations. We predict nanoparticle melting temperatures in good agreement with respect to available experimental data. Furthermore, we characterize in detail the solid to liquid phase change mechanism employing an unsupervised learning scheme to categorize local atomic environments. We thus provide a rigorous and data-driven definition of liquid atomic arrangements in the inner and surface regions of a nanoparticle, and employ it to show that melting initiates at the outer layers. The record contains all the MD simulation trajectories carried out using mapped machine learning force fields ...

Latest version: v1
Publication date: Aug 11, 2021


Local kernel regression and neural network approaches to the conformational landscapes of oligopeptides

DOI10.24435/materialscloud:kp-82

Raimon Fabregat, Alberto Fabrizio, Edgar Engel, Benjamin Meyer, Veronika Juraskova, Michele Ceriotti, Clemence Corminboeuf

  • The application of machine learning to theoretical chemistry has made it possible to combine the accuracy of quantum chemical energetics with the thorough sampling of finite-temperature fluctuations. To reach this goal, a diverse set of methods has been proposed, ranging from simple linear models to kernel regression and highly nonlinear neural networks. Here we apply two widely different approaches to the same, challenging problem - the sampling of the conformational landscape of polypeptides at finite temperature. We develop a Local Kernel Regression (LKR) coupled with a supervised sparsity method and compare it with a more established approach based on Behler-Parrinello type Neural Networks. In the context of the LKR, we discuss how the supervised selection of the reference pool of environments is crucial to achieve accurate potential energy surfaces at a competitive computational cost and leverage the locality of the model to infer which chemical environments are poorly ...

Latest version: v1
Publication date: Aug 10, 2021


Characterization of chemisorbed species and active adsorption sites in Mg-Al mixed metal oxides for high temperature CO2 capture

DOI10.24435/materialscloud:ba-jz

Alicia Lund, Manohara Gudiyor, Ah-Young Song, Kevin Maik Jablonka, Christopher Ireland, Li Anne Cheah, Berend Smit, Susana Garcia, Jeffrey Reimer

  • Mg-Al mixed metal oxides (MMOs), derived from the decomposition of layered double hydroxides (LDHs), have been purposed as a material for CO2 capture of industrial plant emissions. In order to aid in the design and optimization of these materials for CO2 capture at 200 °C, we have used the combination of solid-state nuclear magnetic resonance (ssNMR) and density functional theory (DFT) to characterize the CO2 gas sorption products and determine the various sorption sites in the Mg-Al MMOs. Comparison of DFT cluster calculations with 13C chemical shift of the chemisorbed products indicates that mono and bi-dentate carbonate are formed at the Mg-O site with an adjacent Al substitution of an Mg atom, while bicarbonate is formed at Mg-OH sites without adjacent Al substitution. Quantitative 13C NMR shows an increase in the relative amount of strongly basic sites, where the monodentate carbonate product is formed, with increasing Al mole % in the MMO. This detailed understanding of the ...

Latest version: v1
Publication date: Aug 09, 2021


Crystal-graph attention networks for the prediction of stable materials

DOI10.24435/materialscloud:2b-x9

Jonathan Schmidt, Love Pettersson, Claudio Verdozzi, Silvana Botti, Miguel Marques

  • Graph neural networks have enjoyed great success in the prediction of material properties for both molecules and crystals. These networks typically use the atomic positions (usually expanded in a Gaussian basis) and the atomic species as input. Unfortunately, this information is in general not available when predicting new materials, for which the precise geometrical information is unknown. In this work, we circumvent this problem by predicting the thermodynamic stability of crystal structures without using the knowledge of the precise bond distances. We replace this information with embeddings of graph distances, allowing our networks to be used directly in high-throughput studies based on both composition and crystal structure prototype. Using these embeddings, we combine the newest developments in graph neural networks and apply them to the prediction of the distances to the convex hull. To train these networks, we curate a dataset of over 2 million density-functional ...

Latest version: v1
Publication date: Aug 06, 2021


Approaching disorder-tolerant semiconducting polymers

DOI10.24435/materialscloud:tm-yw

Xinwen Yan, Miao Xiong, Xin-Yu Deng, Kai-Kai Liu, Jia-Tong Li, Xue-Qing Wang, Song Zhang, Nathaniel Prine, Zhuoqiong Zhang, Wanying Huang, Yishan Wang, Jie-Yu Wang, Xiaodan Gu, Shu Kong So, Jia Zhu, Ting Lei*

  • Doping has been widely used to control the charge carrier concentration in organic semiconductors. However, in conjugated polymers, n-doping is often limited by the tradeoff between doping efficiency and charge carrier mobilities, since dopants are often randomly distributed within polymers, leading to significant structural and energetic disorder. Here, we screen a large number of polymer building block combinations and explore the possibility of designing n-type conjugated polymers with good tolerance to dopant-induced disorder. We show that a carefully designed conjugated polymer with a single dominant planar backbone conformation, high torsional barrier at each dihedral angle, and zigzag backbone curvature is highly dopable and can tolerate dopant-induced disorder. With these features, the newly designed diketopyrrolopyrrole (DPP)-based polymer can be efficiently n-doped and exhibit high n-type electrical conductivities over 120 S cm−1, much higher than the reference polymers ...

Latest version: v1
Publication date: Aug 04, 2021


Diversifying databases of metal organic frameworks for high-throughput computational screening

DOI10.24435/materialscloud:yn-de

Sauradeep Majumdar, Seyed Mohamad Moosavi, Kevin Maik Jablonka, Daniele Ongari, Berend Smit

  • By combining metal nodes and organic linkers, an infinite number of metal organic frameworks (MOFs) can be designed in silico. When making new databases of such hypothetical MOFs, we need to assure that they not only contribute towards the growth of the count of structures but also add different chemistry to existing databases. In this work, we designed a database of ~20,000 hypothetical MOFs which are diverse in terms of their chemical design space—metal nodes, organic linkers, functional groups and pore geometries. Using Machine Learning techniques, we visualized and quantified the diversity of these structures. We then assessed the usefulness of diverse structures by evaluating their performance, using grand-canonical Monte Carlo simulations, in two important environmental applications---post combustion carbon capture and hydrogen storage. We find that many of these structures perform better than widely used benchmark materials such as Zeolite-13X (for post combustion carbon capture) and MOF-5 (for hydrogen storage).

Latest version: v1
Publication date: Jul 30, 2021


Efficient and low-scaling linear-response time-dependent density functional theory implementation for core-level spectroscopy of large and periodic systems

DOI10.24435/materialscloud:js-me

Augustin Bussy, Jürg Hutter

  • A new implementation of linear-response time-dependent density functional theory (LR-TDDFT) for core level near-edge absorption spectroscopy is discussed. The method is based on established LR-TDDFT approaches to X-ray absorption spectroscopy (XAS) with additional accurate approximations for increased efficiency. We validate our implementation by reproducing benchmark results at the K-edge and showing that spin–orbit coupling effects at the L2,3-edge are well described. We also demonstrate that the method is suitable for extended systems in periodic boundary conditions and measure a favorable sub-cubic scaling of the calculation cost with system size. We finally show that GPUs can be efficiently exploited and report speedups of up to a factor 2.

Latest version: v1
Publication date: Jul 29, 2021


Hidden bulk and surface effects in the spin polarization of the nodal-line semimetal ZrSiTe

DOI10.24435/materialscloud:pp-qe

G. Gatti, D. Gosálbez-Martínez, S. Roth, M. Fanciulli, M. Zacchigna, M. Kalläne, K. Rossnagel, C. Jozwiak, A. Bostwick, E. Rotenberg, A. Magrez, H. Berger, I. Vobornik, J. Fujii, O. V. Yazyev, M. Grioni, A. Crepaldi

  • In the present record we provide the data obtained in ARPES experiments and input/output files of Quantum ESPRESSO calculations used in the publication entitled as this record. The experimental data consist of the Fermi surface at kz=π/c, the experimental band dispersion along the MΓM, XΓX and XMX, spin-resolved ARPES spectra, and spin-resolved ARPES spectra of surface states. The theoretical data consist in the bulk and slab calculations to support the experimental data.

Latest version: v1
Publication date: Jul 29, 2021


Radial spin texture of the Weyl fermions in chiral tellurium

DOI10.24435/materialscloud:qp-hy

Gianmarco Gatti, Daniel Gosálbez-Martínez, Stepan S. Tsirkin, Mauro Fanciulli, Michele Puppin, Serhii Polishchuk, Simon Moser, Luc Testa, Edoardo Martino, Silvan Roth, Philippe Bugnon, Luca Moreschini, Aaron Bostwick, Chris Jozwiak, Eli Rotenberg, Giovanni Di Santo, Luca Petaccia, Ivana Vobornik, Jun Fujii, Joeson Wong, Deep Jariwala, Harry Atwater, Heinrik Rønnow, Majed Chergui, Oleg Yazyev, Marco Grioni, Alberto Crepaldi

  • Trigonal tellurium, a small-gap semiconductor with pronounced magneto-electric and magneto-optical responses, is among the simplest realizations of a chiral crystal. We have studied by spin- and angle-resolved photoelectron spectroscopy its unconventional electronic structure and unique spin texture. We identify Kramers–Weyl, composite, and accordionlike Weyl fermions, so far only predicted by theory, and show that the spin polarization is parallel to the wave vector along the lines in k space connecting high-symmetry points. Our results clarify the symmetries that enforce such spin texture in a chiral crystal, thus bringing new insight in the formation of a spin vectorial field more complex than the previously proposed hedgehog configuration. Our findings thus pave the way to a classification scheme for these exotic spin textures and their search in chiral crystals. This records refers to the experimental data shown in the referenced article, saved as txt files along with a metadata descriptor file.

Latest version: v1
Publication date: Jul 28, 2021


Light-induced renormalization of the Dirac quasiparticles in the nodal-line semimetal ZrSiSe

DOI10.24435/materialscloud:hh-c1

Gianmarco Gatti, Alberto Crepaldi, Michele Puppin, Nicolas Tancogne-Dejean, Lede Xian, Umberto De Giovannini, Silvan Roth, Serhii Polishchuk, Philippe Bugnon, Arnaud Magrez, Helmuth Berger, Fabio Frassetto, Luca Poletto, Luca Moreschini, Simon Moser, Aaron Bostwick, Eli Rotenberg, Angel Rubio, Majed Chergui, Marco Grioni

  • In nodal-line semimetals, linearly dispersing states form Dirac loops in the reciprocal space with a high degree of electron-hole symmetry and a reduced density of states near the Fermi level. The result is reduced electronic screening and enhanced correlations between Dirac quasiparticles. Here we investigate the electronic structure of ZrSiSe, by combining time- and angle-resolved photoelectron spectroscopy with ab initio density functional theory (DFT) complemented by an extended Hubbard model (DFT+U+V) and by time-dependent DFT+U+V. We show that electronic correlations are reduced on an ultrashort timescale by optical excitation of high-energy electrons-hole pairs, which transiently screen the Coulomb interaction. Our findings demonstrate an all-optical method for engineering the band structure of a quantum material. This record contains the ARPES raw data in txt format used to create the figures in the referenced publication.

Latest version: v1
Publication date: Jul 28, 2021


Computational synthesis of substrates by crystal cleavage

DOI10.24435/materialscloud:tm-js

Joshua Paul, Alice Galdi, Christopher Parzyck, Kyle Shen, Jared Maxson, Richard Hennig

  • In order to identify novel substrate materials, we developed a high-throughput bond breaking algorithm. This algorithm takes a three-dimensional crystal as input, systematically breaks bonds, and checks if the bonding network has been reduced to two periodic directions. We apply this algorithm to Materials Project database and identify 4,693 symmetrically unique cleaved surfaces across 2,133 crystals. We then characterize the thermodynamic stability of these cleaved surfaces using the DFT software VASP, characterizing 3,991 surfaces as potential substrates with energy comparable to the experimentally used substrates (0001) AlN, ZnO, and CdS. This repository contains the structure files, setting files, pseudopotential choices, bulk precursor structure and MaterialsProject ID, and thermodynamic data for the substrates considered in this work.

Latest version: v1
Publication date: Jul 28, 2021


First principles correction scheme for linear-response time-dependent density functional theory calculations of core electronic states

DOI10.24435/materialscloud:r8-tj

Augustin Bussy, Jürg Hutter

  • Linear-response time-dependent density functional theory (LR-TDDFT) for core level spectroscopy using standard local functionals suffers from self-interaction error and a lack of orbital relaxation upon creation of the core hole. As a result, LR-TDDFT calculated X-ray absorption near edge structure (XANES) spectra need to be shifted along the energy axis to match experimental data. We propose a correction scheme based on many body perturbation theory to calculate the shift from first principles. The ionization potential of the core donor state is first computed and then substituted for the corresponding Kohn--Sham orbital energy, thus emulating Koopmans' condition. Both self-interaction error and orbital relaxation are taken into account. The method exploits the localized nature of core states for efficiency and integrates seamlessly in our previous implementation of core level LR-TDDFT, yielding corrected spectra in a single calculation. We benchmark the correction scheme on ...

Latest version: v2
Publication date: Jul 28, 2021


Anti-symmetric Compton scattering in LiNiPO4: Towards a direct probe of the magneto-electric multipole moment

DOI10.24435/materialscloud:yx-7k

Sayantika Bhowal, Daniel O'Neill, Michael Fechner, Nicola A. Spaldin, Urs Staub, Jon Duffy, Stephen P. Collins

  • We present a combined theoretical and experimental investigation of the anti-symmetric Compton profile in LiNiPO4 as a possible probe for magneto-electric toroidal moments. Understanding as well as detecting such magneto-electric multipoles is an active area of research in condensed matter physics. Our calculations, based on density functional theory, indicate an anti-symmetric Compton profile in the direction of the ty toroidal moment in momentum space, with the computed anti-symmetric profile around four orders of magnitude smaller than the total profile. The difference signal that we measure is consistent with the computed profile, but of the same order of magnitude as the statistical errors and systematic uncertainties of the experiment. Our results motivate further theoretical work to understand the factors that influence the size of the anti-symmetric Compton profile, and to identify materials exhibiting larger effects.

Latest version: v1
Publication date: Jul 23, 2021


The importance of nuclear quantum effects for NMR crystallography

DOI10.24435/materialscloud:nj-2g

Edgar A. Engel, Venkat Kapil, Michele Ceriotti

  • The resolving power of solid-state nuclear magnetic resonance (NMR) crystallography depends heavily on the accuracy of the computational prediction of NMR chemical shieldings of candidate structures, which are usually taken to be local minima in the potential energy surface. To test the limits of this approximation, we perform a systematic study of the role of finite-temperature and quantum nuclear fluctuations on 1H, 13C, and 15N chemical shieldings in molecular crystals -- considering the paradigmatic examples of the different polymorphs of benzene, glycine, and succinic acid. We find the effect of quantum fluctuations to be comparable in size to the typical errors of predictions of chemical shieldings for static nuclei with respect to experimental measurements, and to improve the match between experiments and theoretical predictions, translating to more reliable assignment of the NMR spectra to the correct candidate structure. Thanks to the use of integrated machine-learning ...

Latest version: v1
Publication date: Jul 23, 2021


Revealing hidden magneto-electric multipoles using Compton scattering

DOI10.24435/materialscloud:wc-5z

Sayantika Bhowal, Nicola A. Spaldin

  • Magneto-electric multipoles, which are odd under both space-inversion 𝓘 and time-reversal 𝓣 symmetries, are fundamental in understanding and characterizing magneto-electric materials. However, the detection of these magneto-electric multipoles is often not straightforward as they remain "hidden" in conventional experiments in part since many magneto-electrics exhibit combined 𝓘𝓣 symmetry. In the present work, we show that the anti-symmetric Compton profile is a unique signature for all the magneto-electric multipoles, since the asymmetric magnetization density of the magneto-electric multipoles couples to space via spin-orbit coupling, resulting in an anti-symmetric Compton profile. We develop the key physics of the anti-symmetric Compton scattering using symmetry analysis and demonstrate it using explicit first-principles calculations for two well-known representative materials with magneto-electric multipoles, insulating LiNiPO₄ and metallic Mn₂Au. Our work emphasizes the ...

Latest version: v1
Publication date: Jul 23, 2021


In situ inorganic conductive network enables superior high-voltage operation of single-crystal Ni-rich cathode

DOI10.24435/materialscloud:ga-f0

Xinming Fan, Xing Ou, Wengao Zhao, Yun Liu, Bao Zhang, Jiafeng Zhang, Lianfeng Zou, Lukas Seidl, Yangzhong Li, Guorong Hu, Corsin Battaglia, Yong Yang

  • High nickel content in LiNixCoyMnzO2 (NCM, x ≥ 0.8, x + y + z = 1) layered cathode material allows high energy density in lithium-ion batteries (LIBs). However, Ni-rich NCM cathodes suffer from performance degradation, mechanical and structural instability upon prolonged cell cycling. Although the use of single-crystal Ni-rich NCM can mitigate these drawbacks, the ion-diffusion in large single-crystal particles hamper its rate capability. Herein, we report a strategy to construct an in situ Li1.4Y0.4Ti1.6(PO4)3 (LYTP) ion/electron conductive network which interconnects single-crystal LiNi0.88Co0.09Mn0.03O2 (SC-NCM88) particles. The LYTP network facilitates the lithium-ion transport between SC-NCM88 particles, mitigates mechanical instability and prevents detrimental crystalline phase transformation. When used in combination with a Li metal anode, the LYTP-containing SC-NCM88-based cathode enables a coin cell capacity of 130 mAh g-1 after 500 cycles at 5 C rate in the 2.75-4.4 V ...

Latest version: v1
Publication date: Jul 21, 2021


Differentiable sampling of molecular geometries with uncertainty-based adversarial attacks

DOI10.24435/materialscloud:2w-6h

Daniel Schwalbe-Koda, Aik Rui Tan, Rafael Gómez-Bombarelli

  • Neural network (NN) force fields can predict potential energy surfaces with high accuracy and speed compared to electronic structure methods typically used to generate their training data. However, NN predictions are well-defined only for points close to the training domains, and may exhibit poor results during extrapolation. Uncertainty quantification methods can detect geometries for which predicted errors are high, but sampling regions of high uncertainty requires a thorough exploration of the phase space, often using expensive simulations. Our work uses automatic differentiation to sample atomistic configurations by balancing thermodynamic accessibility and uncertainty quantification without using molecular dynamics simulations. This dataset provides the atomistic data used to train the NN potentials for the ammonia, alanine dipeptide, and zeolite-molecule systems. For all materials, geometries, energies, and forces are provided. The ammonia and zeolite systems were computed ...

Latest version: v1
Publication date: Jul 20, 2021


Electronic structure of water from Koopmans-compliant functionals

DOI10.24435/materialscloud:76-zf

James Moraes de Almeida, Ngoc Linh Nguyen, Nicola Colonna, Wei Chen, Caetano Rodrigues Miranda, Alfredo Pasquarello, Nicola Marzari

  • Obtaining a precise theoretical description of the spectral properties of liquid water poses challenges for both molecular dynamics (MD) and electronic structure methods. The lower computational cost of the Koopmans-compliant functionals with respect to Green’s function methods allows the simulations of many MD trajectories, with a description close to the state-of-art quasi-particle self-consistent GW plus vertex corrections method (QSGW + fxc). Thus, we explore water spectral properties when different MD approaches are used, ranging from classical MD to first-principles MD, and including nuclear quantum effects. We have observed that different MD approaches lead to up to 1 eV change in the average band gap; thus, we focused on the band gap dependence with the geometrical properties of a system to explain such spread. We have evaluated the changes in the band gap due to variations in the intramolecular O–H bond distance and HOH angle, as well as the intermolecular hydrogen bond ...

Latest version: v2
Publication date: Jul 20, 2021


Reconstruction of Bloch wavefunctions of holes in a semiconductor

DOI10.24435/materialscloud:m0-t8

J. B. Costello, S. D. O'Hara, Q. Wu, D. C. Valovcin, L. N. Pfeiffer, K. W. West, M. S. Sherwin

  • A central goal of condensed matter physics is to understand the rich and diverse electronic and optical properties that emerge as wavelike electrons move through the periodically-arranged atoms in crystalline materials. However, more than 90 years after Bloch derived the functional forms of electronic waves in crystals (now known as Bloch wavefunctions) rapid scattering processes have so far prevented their direct experimental reconstruction. In high-order sideband generation (HSG), electrons and holes generated in semiconductors by a near-infrared (NIR) laser are accelerated to high kinetic energy by a strong terahertz field, and recollide to emit NIR sidebands before they are scattered. Here we reconstruct the Bloch wavefunctions of two types of holes in gallium arsenide wavelengths much longer than the spacing between atoms by experimentally measuring sideband polarizations and introducing an elegant theory that ties those polarizations to quantum interference between different ...

Latest version: v1
Publication date: Jul 20, 2021


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