Recommended by

Indexed by

Latest records

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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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

Invariance principles in the theory and computation of transport coefficients


Federico Grasselli, Stefano Baroni

  • In this work we elaborate on recently discovered invariance principles, according to which transport coefficients are, to a large extent, independent of the microscopic definition of the densities and currents of the conserved quantities being transported (energy, momentum, mass, charge). These invariance principles can be combined with new spectral analysis methods for the current time series to be fed into the Green-Kubo formula to obtain accurate estimates of transport coefficients from relatively short molecular dynamics simulations. In this record we collect the time series of the ab initio charge flux for a simulation of molten potassium chloride, together with the Jupyter Notebooks we employed to analyse the data and produce the figures in the related article.

Latest version: v1
Publication date: Jul 19, 2021

Coherent energy exchange between carriers and phonons in Peierls-distorted bismuth unveiled by broadband XUV pulses


Romain Géneaux, Iurii Timrov, Christopher Kaplan, Andrew Ross, Peter Kraus, Stephen Leone

  • In Peierls-distorted materials, photoexcitation leads to a strongly coupled transient response between structural and electronic degrees of freedom, always measured independently of each other. Here we use transient reflectivity in the extreme ultraviolet to quantify both responses in photoexcited bismuth in a single measurement. With the help of first-principles calculations based on density-functional theory (DFT) and time-dependent DFT, the real-space atomic motion and the temperature of both electrons and holes as a function of time are captured simultaneously, retrieving an anticorrelation between the A1g phonon dynamics and carrier temperature. The results reveal a coherent, bi-directional energy exchange between carriers and phonons, which is a dynamical counterpart of the static Peierls-Jones distortion, providing first-time validation of previous theoretical predictions.

Latest version: v1
Publication date: Jul 16, 2021

Effects of interlayer confinement and hydration on capacitive charge storage in birnessite


Shelby Boyd, Karthik Ganeshan, Wan-Yu Tsai, Tao Wu, Saeed Saeed, De-en Jiang, Nina Balke, Adri van Duin, Veronica Augustyn

  • Nanostructured birnessite (δ-MnO2) exhibits high specific capacitance and nearly ideal capacitive behavior in aqueous electrolytes, rendering it an important electrode material for low-cost, high power energy storage devices. The mechanism of electrochemical capacitance in birnessite has been described as both faradaic (involving redox) and non-faradaic (involving only electrostatic interactions). To clarify the capacitive mechanism, we characterized birnessite’s response to applied potential using ex situ X-ray diffraction, electrochemical quartz crystal microbalance, in situ Raman spectroscopy, and operando atomic force microscopy dilatometry to provide a holistic understanding of its structural, gravimetric, and mechanical response. These observations are supported by atomic-scale simulations using density functional theory for the cation-intercalated structure of birnessite and ReaxFF-based molecular dynamics, as well as ReaxFF-based grand canonical Monte Carlo simulations on ...

Latest version: v1
Publication date: Jul 16, 2021

Importance of intersite Hubbard interactions in β-MnO2: A first-principles DFT+U+V study


Ruchika Mahajan, Iurii Timrov, Nicola Marzari, Arti Kashyap

  • We present a first-principles investigation of the structural, electronic, and magnetic properties of pyrolusite (β-MnO2) using conventional and extended Hubbard-corrected density-functional theory (DFT+U and DFT+U+V). The onsite U and intersite V Hubbard parameters are computed using linear-response theory in the framework of density-functional perturbation theory. We show that while the inclusion of the onsite U is crucial to describe the localized nature of the Mn(3d) states, the intersite V is key to capture accurately the strong hybridization between neighboring Mn(3d) and O(2p) states. In this framework, we stabilize the simplified collinear antiferromagnetic (AFM) ordering (suggested by the Goodenough-Kanamori rule) that is commonly used as an approximation to the experimentally-observed noncollinear screw-type spiral magnetic ordering. A detailed investigation of the ferromagnetic and of other three collinear AFM spin configurations is also presented. The findings from ...

Latest version: v1
Publication date: Jul 16, 2021

Structure and energetics of dye-sensitized NiO interfaces in water from ab-initio MD and large-scale GW calculations


Alekos Segalina, Sébastien Lèbegue, Dario Rocca, Simone Piccinin, Mariachiara Pastore

  • The energy level alignment across solvated molecule/semiconductor interfaces is a crucial property for the correct functioning of dye-sensitized photo-electrodes, where, following the absorption of solar light, a cascade of interfacial hole/electron transfer processes has to efficiently take place. In light of the difficulty of performing X-ray photoelectron spectroscopy measurements at the molecule/solvent/metal-oxide interface, being able to accurately predict the level alignment by first-principles calculations on realistic structural models would represent an important step toward the optimization of the device. In this respect dye/NiO surfaces, employed in p-type dye-sensitized solar cells, are undoubtedly challenging for ab initio methods and, also for this reason, much less investigated than the n-type dye/TiO2 counterpart. Here we consider the C343-sensitized NiO surface in water and combine ab initio Molecular Dynamics (AIMD) simulations with GW (G0W0) calculations, ...

Latest version: v1
Publication date: Jul 16, 2021

Machine learning for metallurgy: a neural network potential for Al-Cu-Mg


Daniel Marchand, W.A. Curtin

  • High-strength metal alloys achieve their performance via careful control of precipitates and solutes. The nucleation, growth, and kinetics of precipitation, and the resulting mechanical properties, are inherently atomic-scale phenomena, particularly during early-stage nucleation and growth. Atomistic modeling using interatomic potentials is a desirable tool for understanding the detailed phenomena involved in precipitation and strengthening, which requires length and time scales far larger than those accessible by first-principles methods. Current interatomic potentials for alloys are not, however, sufficiently accurate for such studies. Here, a family of neural-network potentials (NNPs) for the Al-Cu-Mg system is presented as the first example of a machine-learning potential that can achieve near-first-principles accuracy for many different metallurgically-important aspects of this alloy. High fidelity predictions of intermetallic compounds, elastic constants, dilute ...

Latest version: v1
Publication date: Jul 14, 2021

The importance of reference frame for pressure at the liquid-vapour interface


Edward R. Smith

  • This repository has the input files and a guide to recreate the data from "The importance of reference frame for pressure at the liquid-vapour interface" (https://arxiv.org/abs/2107.00499). It requires the Flowmol code to be downloaded and built from https://github.com/edwardsmith999/flowmol (it should work with the latest version but the paper was generated from commit c4a52d434053d676c0281449b0fce7112116fd54 or the persistent version linked to DOI https://doi.org/10.5281/zenodo.4639546). The included README.txt file outlines how to do this. The input files are also included on the Github repository. The summarised data is also included as a Python pickle (summary.p) with scripts to produce all plots from the paper. This data, which shows the profile going through a liquid vapour interface, can be analysed in Python. The abstract for the article, which explains the importance of this data, is as follows: The local pressure tensor is non-unique, a fact which has generated ...

Latest version: v1
Publication date: Jul 14, 2021

A microscopic picture of paraelectric perovskites from structural prototypes


Michele Kotiuga, Samed Halilov, Boris Kozinsky, Marco Fornari, Nicola Marzari, Giovanni Pizzi

  • This work details how to determine structural prototypes for the cubic perovskite structure that are used to study the B-site displacements in the cubic, paraelectric phase. Car-Parrinello MD simulations of cubic barium titanate (BaTiO3) show the titanium displacements from the undistorted cubic structure. Using a systematic symmetry analysis we construct microscopic templates, i.e. representative structural models in the form of supercells that satisfy a desired point symmetry but are built from the combination of lower-symmetry primitive cells. Density functional theory calculations, using the microscopic templates as starting structures for a relaxation, are carried out to find structural prototypes of BaTiO3 with local polar distortions but with cubic point symmetry. The stability of these structures is studied as a function of volume and with respect to the zone-boundary phonons of pristine cubic BaTiO3. The stable distortions patterns for BaTiO3 are investigated for other titanates and for a handful of niobates and zirconates.

Latest version: v1
Publication date: Jul 12, 2021

Zeo-1: A computational data set of zeolite structures


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: v1
Publication date: Jul 07, 2021

Exploding and weeping ceramics


Hanlin Gu, Jascha Rohmer, Justin Jetter, Andriy Lotnyk, Lorenz Kienle, Eckhard Quandt, Richard D. James

  • The systematic tuning of the lattice parameters to achieve improved kinematic compatibility between phases is a broadly effective strategy for improving the reversibility, and lowering the hysteresis, of solid-solid phase transformations. Here, “kinematic compatibility” refers to the fitting together of the phases. We present an apparently paradoxical example in which tuning to near perfect compatibility in (Zr/Hf)O2-(YNb)O4 results in a high degree of irreversibility, as manifested in explosive or “weeping” behavior on cooling through the tetragonal-to-monoclinic phase transformation. In the case of weeping the polycrystal slowly and steadily falls apart at the grain boundaries. These effects occur without chemical change. Finally, tuning to satisfy a condition we term the equidistance condition results in reversible behavior with the lowest hysteresis in this system. We give evidence that all these observations are explained by a more careful analysis of compatibility of the ...

Latest version: v1
Publication date: Jul 05, 2021

Interplay between polarization, strain and defect-pairs in Fe-doped SrMnO3-δ


Chiara Ricca, Ulrich Aschauer

  • Defect chemistry, strain, and structural, magnetic and electronic degrees of freedom constitute a rich space for the design of functional properties in transition metal oxides. Here, we show that it is possible to engineer polarity and ferroelectricity in non-polar perovskite oxides via polar defect pairs formed by anion vacancies coupled to substitutional cations. We use a self-consistent site-dependent DFT+U approach that accounts for local structural and chemical changes upon defect creation and which is crucial to reconcile predictions with the available experimental data. Our results for Fe-doped oxygen-deficient SrMnO3 show that substitutional Fe and oxygen vacancies can promote polarity due to an o -center displacement of the defect charge resulting in a net electric dipole moment, which polarizes the lattice in the defect neighborhood. The formation of these defects and the resulting polarization can be tuned by epitaxial strain, resulting in enhanced polarization also for ...

Latest version: v1
Publication date: Jul 01, 2021

Building a consistent and reproducible database for adsorption evaluation in Covalent-Organic Frameworks


Daniele Ongari, Aliaksandr V. Yakutovich, Leopold Talirz, Berend Smit

  • We present a workflow that traces the path from the bulk structure of a crystalline material to assessing its performance in carbon capture from coal’s postcombustion flue gases. This workflow is applied to a database of 324 covalent−organic frameworks (COFs) reported in the literature, to characterize their CO2 adsorption properties using the following steps: (1) optimization of the crystal structure (atomic positions and unit cell) using density functional theory, (2) fitting atomic point charges based on the electron density, (3) characterizing the pore geometry of the structures before and after optimization, (4) computing carbon dioxide and nitrogen isotherms using grand canonical Monte Carlo simulations with an empirical interaction potential, and finally, (5) assessing the CO2 parasitic energy via process modeling. The full workflow has been encoded in the Automated Interactive Infrastructure and Database for Computational Science (AiiDA). Both the workflow and the ...

Latest version: v9
Publication date: Jun 30, 2021

Observation of a singular Weyl point surrounded by charged nodal walls in PtGa


Junzhang Ma, Quansheng Wu, Meng Song, Shengnan Zhang, E.B. Guedes, S.A. Ekahana, M. Krivenkov, Mengyu Yao, Shunye Gao, Wenhui Fan, Tian Qian, Hong Ding, N.C. Plumb, Milan Radovic, J. H. Dil, Yimin Xiong, K. Manna, C. Felser, Oleg Yazyev, Ming Shi

  • This record contains all the raw data in the paper Nature Communications volume 12, Article number: 3994 (2021). Constrained by the Nielsen-Ninomiya no-go theorem, in all so-far experimentally determined Weyl semimetals (WSMs) the Weyl points (WPs) always appear in pairs in the momentum space with no exception. As a consequence, Fermi arcs occur on surfaces which connect the projections of the WPs with opposite chiral charges. However, this situation can be circumvented in the case of unpaired WP, without relevant surface Fermi arc connecting its surface projection, appearing singularly, while its Berry curvature field is absorbed by nontrivial charged nodal walls. Here, combining angle-resolved photoemission spectroscopy with density functional theory calculations, we show experimentally that a singular Weyl point emerges in PtGa at the center of the Brillouin zone (BZ), which is surrounded by closed Weyl nodal walls located at the BZ boundaries and there is no Fermi arc ...

Latest version: v1
Publication date: Jun 30, 2021

High-throughput calculation of interlayer van der Waals force validated with experimental measurements


Kewei Tang, Weihong Qi, Yaru Wei, Guoliang Ru, Weimin Liu

  • Interlayer binding strength is an important property of two-dimensional (2D) materials in various occasions including exfoliation and heterostructure construction. Though there are already many calculations and experimental measurements for interlayer binding energy, few calculation references regarding the interlayer binding force can be found which is often the quantity been directly measured in experiments. Moreover, binding force rather than binding energy should be considered more closely related to whether a layered structure can be exfoliated or not under certain circumstances. To our best knowledge, there exists no such a database for 2D materials interlayer binding forces. In this work, with a descent algorithm designed to work with first-principles code, maximum interlayer binding force with the accuracy down to 1 meV/Å per atom is directly calculated for 230 common 2D materials using both the vdW-DF2 and optB88-vdW functionals. The results show significant inconsistency ...

Latest version: v1
Publication date: Jun 30, 2021

Band gaps of liquid water and hexagonal ice through advanced electronic-structure calculations


Thomas Bischoff, Igor Reshetnyak, Alfredo Pasquarello

  • The fundamental band gaps of liquid water and hexagonal ice are calculated through advanced electronic-structure methods. We compare specifically the performance of state-of-the-art GW calculations with nonempirical hybrid functionals. For the latter, we fix the free parameters either through the dielectric response of the material or through enforcing Koopmans' condition to localized states. The various approaches yield consistent band gaps, in good agreement with available experimental references. Furthermore, we discuss the critical aspects of each approach that underlie the band-gap predictions.

Latest version: v1
Publication date: Jun 28, 2021

Impact of quantum-chemical metrics on the machine learning prediction of electron density


Ksenia R. Briling, Alberto Fabrizio, Clemence Corminboeuf

  • Machine learning (ML) algorithms have undergone an explosive development impacting every aspect of computational chemistry. To obtain reliable predictions, one needs to maintain the proper balance between the black-box nature of ML frameworks and the physics of the target properties. One of the most appealing quantum-chemical properties for regression models is the electron density, and some of us recently proposed a transferable and scalable model based on the decomposition of the density onto an atom-centered basis set. The decomposition, as well as the training of the model, is at its core a minimization of some loss function, which can be arbitrarily chosen and may lead to results of different quality. Well-studied in the context of density fitting (DF), the impact of the metric on the performance of ML models has not been analyzed yet. In this work, we compare predictions obtained using the overlap and the Coulomb repulsion metrics for both the decomposition and training. As ...

Latest version: v1
Publication date: Jun 28, 2021

Modeling the Ga/As binary system across temperatures and compositions from first principles


Giulio Imbalzano, Michele Ceriotti

  • Materials composed of elements from the third and fifth columns of the periodic table display a very rich behavior, with the phase diagram usually containing a metallic liquid phase and a polar semiconducting solid. As a consequence, it is very hard to achieve transferable empirical models of interactions between the atoms that can reliably predict their behavior across the temperature and composition range that is relevant to the study of the synthesis and properties of III/V nanostructures and devices. We present a machine-learning potential trained on density functional theory reference data that provides a general-purpose model for the Ga/As system. We provide a series of stringent tests that showcase the accuracy of the potential, and its applicability across the whole binary phase space, computing with ab initio accuracy a large number of finite-temperature properties as well as the location of phase boundaries. We also show how a committee model can be used to reliably ...

Latest version: v1
Publication date: Jun 28, 2021

First-principles predictions of Hall and drift mobilities in semiconductors


Samuel Poncé, Francesco Macheda, Elena Roxana Margine, Nicola Marzari, Nicola Bonini, Feliciano Giustino

  • Carrier mobility is one of the defining properties of semiconductors. Significant progress on parameter-free calculations of carrier mobilities in real materials has been made during the past decade; however, the role of various approximations remains unclear and a unified methodology is lacking. Here, we present and analyse a comprehensive and efficient approach to compute the intrinsic, phonon-limited drift and Hall carrier mobilities of semiconductors, within the framework of the first-principles Boltzmann transport equation. The methodology exploits a novel approach for estimating quadrupole tensors and including them in the electron-phonon interactions, and capitalises on a rigorous and efficient procedure for numerical convergence. The accuracy reached in this work allows to assess common approximations, including the role of exchange and correlation functionals, spin-orbit coupling, pseudopotentials, Wannier interpolation, Brillouin-zone sampling, dipole and quadrupole ...

Latest version: v1
Publication date: Jun 25, 2021

Ferroelectricity promoted by cation/anion divacancies in SrMnO3


Chiara Ricca, Danielle Berkowitz, Ulrich Aschauer

  • We investigate the effect of polar Sr-O vacancy pairs on the electric polarization of SrMnO3 (SMO) thin films using density functional theory (DFT) calculations. This is motivated by indications that ferroelectricity in complex oxides can be engineered by epitaxial strain but also via the defect chemistry. Our results suggest that intrinsic doping by cation and anion divacancies can induce a local polarization in unstrained non-polar SMO thin films and that a ferroelectric state can be stabilized below the critical strain of the stoichiometric material. This polarity is promoted by the electric dipole associated with the defect pair and its coupling to the atomic relaxations upon defect formation that polarize a region around the defect. This suggests that polar defect pairs affect the strain-dependent ferroelectricity in semiconducting antiferromagnetic SMO. For metallic ferromagnetic SMO we find a much weaker coupling between the defect dipole and the polarization due to much ...

Latest version: v1
Publication date: Jun 24, 2021

Effect of density, phonon scattering and nanoporosity on the thermal conductivity of anisotropic cellulose nanocrystal foams


Varvara Apostolopoulou-Kalkavoura, Pierre Munier, Lukasz Dlugozima, Veit-Lorenz Heuthe, Lennart Bergström

  • Ice templated anisotropic foams based on cellulose nanocrystals (CNC) with densities ranging between 25 to 130 kg.m-3 were prepared from aqueous CNC dispersions. The thermal conductivities perpendicular to the columnar macropores direction increased in a non-monotonous way with the increasing CNC foam density while the thermal conductivity reached a minimum value for the CNC foam with the highest nanoporosity. Theoretical calculations including the solid and gas conduction within the foams as well as the thermal conductivity of water showed that phonon scattering at the solid-solid interfaces is responsible for reaching low thermal conductivity values. The foam wall nanoporosity, the particle alignment, the macropores orientation and the foam wall thickness seem to have a minimal effect on the thermal conductivity but can explain the deviations between the theoretical estimates and the experimental data. To this end the identification of the important influencing factors and the ...

Latest version: v2
Publication date: Jun 24, 2021

Chemistry of oxygen ionosorption on SnO2 surfaces


Kostiantyn Sopiha, Oleksandr Malyi, Clas Persson, Ping Wu

  • Ionosorbed oxygen is the key player in reactions on metal-oxide surfaces. This is particularly evident for chemiresistive gas sensors, which operate by modulating the conductivity of active materials through the formation/removal of surface O-related acceptors. Herein, we carried out a detailed study of various charged oxygen species on three naturally occurring surfaces of SnO2. We employed first-principles calculations and revealed that two types of surface acceptors can form spontaneously upon the adsorption of atmospheric oxygen: (i) superoxide O2 (in 1- charged state) on the (110) and the (101) surfaces and (ii) doubly ionized O (in 2- charged state) on the (100) facet, with the experimental evidence pointing to the latter as the source of sensing response. In this dataset, we present the optimized geometries (in CIF format) of different O and O_2 adsorption configurations in the most relevant charged states.

Latest version: v1
Publication date: Jun 22, 2021

Ultrasonic spray coating of polyethylenimine (ethoxylated) as electron injection and transport layer for organic light emitting diodes


Inge Verboven, Rachith Shanivarasanthe Nithyananda Kumar, Melissa Van Landeghem, Hilde Pellaers, Bart Ruttens, Jan D’Haen, Koen Vandewal, Wim Deferme

  • The lighting of the future is expected to be light weight, flexible, highly efficient, non-expensive and fabricated in an environmentally friendly way. Organic light emitting diodes meet all these requirements and can be fabricated using inexpensive and roll-to-roll compatible printing techniques. They however often use low work function, highly reactive metals, such as barium and calcium to facilitate electron injection, deposited using expensive and non-continuous vacuum techniques. Efficient and stable alternatives can be found in the aliphatic amines, polyethylenimine and polyethylenimine(ethoxylated), which shift the work function of aluminum favorably for electron injection. This work demonstrates ultrasonic spray coating of polyethylenimine and polyethylenimine(ethoxylated) as electron injection and transport layer for OLEDs, reducing the work function of the aluminum cathode by 0.355 eV allowing a luminous efficacy comparable to that of the OLEDs using calcium/aluminum ...

Latest version: v1
Publication date: Jun 21, 2021

Enhancing sub-bandgap external quantum efficiency by photomultiplication for narrowband organic near-infrared photodetectors


Jonas Kublitski, Axel Fischer, Shen Xing, Lukasz Baisinger, Eva Bittrich, Johannes Benduhn, Donato Spoltore, Koen Vandewal, Karl Leo

  • Detection of electromagnetic signals for applications such as health, product quality monitoring or astronomy requires highly responsive and wavelength selective devices. Photomultiplication-type organic detectors (PM-OPDs) have shown to achieve high quantum efficiencies mainly in the visible range. Much less research has been focused on realizing near-infrared narrowband PM-OPDs. Here, we demonstrate fully vacuum-processed narrow- and broadband PM‑OPDs. Our devices are based on enhanced hole injection leading to a maximum external quantum efficiency (EQE) of almost 2000% at -10 V for the broadband device. The photomultiplicative effect is also observed in the charge-transfer (CT) state absorption region. By making use of an optical cavity device architecture, we enhance CT absorption and demonstrate a wavelength tunable narrowband PM-OPD with EQEs superior to those of pin‑devices. The presented concept can further improve the performance of state-of-the-art OPDs based on the ...

Latest version: v1
Publication date: Jun 21, 2021

Basic density, lignin content and cleavage strength of Eucalyptus grandis wood


Bruno Soares, José Tarcísio Lima, Claudineia Assis

  • Information about the influence of basic density and lignin content on the propensity of wood to checks, simulated in a cleavage mechanical test, is scarce in the literature. Therefore, the objective of this research was to investigate the functional relationships between the cleavage strength and the basic density and lignin content of the wood. For this, two Eucalyptus grandis trees were felled at 22 years of age and specimens for the cleavage test were made. From these specimens, the basic density and lignin content were determined. The basal logs were sawn for making 45 specimens, 22 from the tree “A” and 23 from the tree “B”. The production of the specimens followed the suggestions of the ASTM D143 standard (ASTM 2014), being free from any defects that could mask the test results, without distinction of heartwood and sapwood or juvenile and mature wood. The mechanical test was carried out with aid of a universal testing machine EMIC, model DL 30000. The 45 specimens tested in ...

Latest version: v1
Publication date: Jun 20, 2021

Chemical stability of hydrogen boride nanosheets in water


Kurt Irvin Rojas, Nguyen Thanh Cuong, Hiroaki Nishino, Ryota Ishibiki, Shin-ichi Ito, Masahiro Miyauchi, Yoshitaka Fujimoto, Satoshi Tominaka, Susumu Okada, Hideo Hosono, Nelson Jr., Arboleda, Takahiro Kondo, Yoshitada Morikawa, Ikutaro Hamada

  • Hydrogen boride sheet is a recently fabricated boron-based two-dimensional nanosheet. For the interest of using it in electronic and catalytic applications, it is important that it has sufficient chemical stability for common substances. In this case, we investigate its chemical stability in water, a common substance in ambient condition and many applications. The study was done using experimental and first-principles method. This record contains the crystal structures, optimized via first-principles calculations that were used in discussing the various properties and interaction between water and hydrogen boride sheet. Additionally, input files used to calculate for the systems were included to aid in reproducing results of the study.

Latest version: v1
Publication date: Jun 19, 2021

Learning the exciton properties of azo-dyes


Alberto Fabrizio, Sergi Vela, Ksenia R. Briling, Clemence Corminboeuf

  • The ab initio determination of the character and properties of electronic excited states (ES) is the cornerstone of modern theoretical photochemistry. Yet, traditional ES methods become readily impractical when applied to fairly large molecules, or when used on thousands of different systems. In contrast, Machine Learning (ML) techniques have demonstrated their accuracy at retrieving ES properties of large molecular databases at a reduced computational cost. Especially for excited states applications, non-linear algorithms tend to be specialized and to target only individual properties. Learning fundamental quantum chemical objects potentially represents a more efficient, yet complex, alternative as a large number of molecular properties could be then extracted through post-processing. Herein, we report the general framework able to learn three fundamental objects of an ES: the hole and particle densities, as well as the transition density. We demonstrate the advantages of ...

Latest version: v1
Publication date: Jun 19, 2021

Koopmans spectral functionals: an open-source periodic-boundary implementation


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

  • Koopmans' spectral functionals aim to describe simultaneously ground state properties and charged excitations of atoms, molecules, nanostructures and periodic crystals. This is achieved augmenting standard density functionals with simple but physically motivated orbital-density-dependent corrections. These corrections act on a set of localized orbitals that, in periodic systems, resembles maximally localized Wannier function. At variance with a direct supercell implementation, we discuss here i) the complex but efficient formalism required for a periodic-boundary code using explicit Brillouin zone sampling, and ii) the calculation of the screened Koopmans' corrections with density-functional perturbation theory. The implementation in the Quantum ESPRESSO distribution and the application to prototypical insulating and semiconducting systems are presented and discussed.

Latest version: v1
Publication date: Jun 01, 2021

Reaction pathway for coke-free methane steam reforming on a Ni/CeO2 catalyst: Active sites and role of metal-support interactions


Agustín Salcedo, Pablo G. Lustemberg, Ning Rui, Robert M. Palomino, Zongyuan Liu, Slavomir Nemsak, Sanjaya D. Senanayake, José A. Rodriguez, M. Verónica Ganduglia-Pirovano, Beatriz Irigoyen

  • Methane steam reforming (MSR) plays a key role in the production of syngas and hydrogen from natural gas. The increasing interest in the use of hydrogen for fuel cell applications demands the development of catalysts with high activity at reduced operating temperatures. Ni-based catalysts are promising systems because of their high activity and low cost, but coke formation generally poses a severe problem. Studies of ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) indicate that CH4/H2O gas mixtures react with Ni/CeO2(111) surfaces to form OH, CHx and CHxO at 300 K. All these species are easy to form and desorb at temperatures below 700 K when the rate of the MSR process accelerates. Density functional theory (DFT) modeling of the reaction over ceria-supported small Ni nanoparticles predicts relatively low activation barriers between 0.3–0.7 eV for the complete dehydrogenation of methane to carbon and the barrierless activation of water at interfacial Ni sites. Hydroxyls ...

Latest version: v1
Publication date: Jun 01, 2021

Computational design of moiré assemblies aided by artificial intelligence


Georgios Tritsaris, Stephen Carr, Gabriel R. Schleder

  • Two-dimensional (2D) layered materials offer a materials platform with potential applications from energy to information processing devices. Although some single- and few-layer forms of materials such as graphene and transition metal dichalcogenides have been realized and thoroughly studied, the space of arbitrarily layered assemblies is still mostly unexplored. The main goal of this work is to demonstrate precise control of layered materials' electronic properties through careful choice of the constituent layers, their stacking, and relative orientation. Physics-based and AI-driven approaches for the automated planning, execution, and analysis of electronic structure calculations are applied to layered assemblies based on prototype one-dimensional (1D) materials and realistic 2D materials. We find it is possible to routinely generate moiré band structures in 1D with desired electronic characteristics such as a band gap of any value within a large range, even with few layers and ...

Latest version: v1
Publication date: Jun 01, 2021

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


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 13,358 entries on aluminum alloy compositions extracted from academic literature and US patents using text processing techniques, in addition to 93 wrought aluminum alloys which are already registered with the Aluminum Association. The second dataset contains 1,268 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: v1
Publication date: Jun 01, 2021

Porous functionalized polymers enable generating and transporting hyperpolarized mixtures of metabolites


Théo El Darai, Samuel Cousin, Quentin Stern, Morgan Ceillier, James Kempf, Dmitry Eshchenko, Roberto Melzi, Marc Schnell, Laurent Gremillard, Aurélien Bornet, Jonas Milani, Basile Vuichoud, Olivier Cala, Damien Montarnal, Sami Jannin

  • Hyperpolarization by dissolution dynamic nuclear polarization (dDNP) has enabled promising applications in spectroscopy and imaging, but remains poorly widespread due to experimental complexity. Broad democratization of dDNP would require remote preparation and distribution of hyperpolarized samples from dedicated facilities. We describe here new hyperpolarizing polymers (HYPOPs) that can generate radical- and contaminant-free hyperpolarized samples within minutes with lifetimes exceeding hours in the solid state. HYPOPs feature tunable macroporous porosity, with porous volumes up to 80% and concentration of nitroxide radicals grafted in the bulk matrix up to 285 μmol g-1. Analytes can be efficiently impregnated as aqueous/alcoholic solutions and hyperpolarized up to P(13C) =25% within 8 min, through the combination of 1H spin diffusion and 1H →13C cross polarization. Solutions of 13C-analytes of biological interest hyperpolarized in HYPOPs display a very long solid-state 13C ...

Latest version: v1
Publication date: May 31, 2021

The nature of the active sites on Ni/CeO2 catalysts for methane conversions


Pablo G. Lustemberg, Zhongtian Mao, Agustín Salcedo, Beatriz Irigoyen, M. Verónica Ganduglia-Pirovano, Charles T. Campbell

  • Effective catalysts for the direct conversion of methane to methanol and for methane’s dry reforming to syngas are Holy Grails of catalysis research toward clean energy technologies. It has recently been discovered that Ni at low loadings on CeO2 is very reactive towards reactants CH4, H2O and CO2 and active for both of these reactions. Revealing the nature of the active sites in such systems is paramount to a rational design of improved catalysts. Here, using a combination of experimental measurements and density functional theory calculations, we show that the most active sites are cationic Ni atoms in clusters at step edges on the CeO2 surface, using the activation of CH4 as an example . We show that the size and morphology of the supported nanoparticles together with strong Ni−support bonding and charge transfer at the step edge are key to the high catalytic activity towards these methane conversions. We anticipate that this knowledge will inspire the development of more efficient catalysts for these reactions.

Latest version: v1
Publication date: May 21, 2021

Simulating solvation and acidity in complex mixtures with first-principles accuracy: the case of CH₃SO₃H and H₂O₂ in phenol


Kevin Rossi, Veronika Juraskova, Raphael Wischert, Laurent Garel, Clemence Corminboeuf, Michele Ceriotti

  • Set of inputs to perform the calculations reported in the paper. The i-pi input enables to perform molecular dynamics / metadynamics / REMD / PIMD simulations, with adequate thermostats. The DFTB and LAMMPS input respectively enable to calculate force and energies within the DFTB and Neural Network Forcefield frameworks. The CP2K input files enable to calculate force and energies at PBE and PBE0 level. The latter is used as the reference to train the neural network correction on top of DFTB. Brief description of the work: We present a generally-applicable computational framework for the efficient and accurate characterization of molecular structural patterns and acid properties in explicit solvent using H₂O₂ and CH₃SO₃H in phenol as an example. In order to address the challenges posed by the complexity of the problem, we resort to a set of data-driven methods and enhanced sampling algorithms. The synergistic application of these techniques makes the first-principle estimation of ...

Latest version: v4
Publication date: May 21, 2021

A Standard Solid State Pseudopotentials (SSSP) library optimized for precision and efficiency


Gianluca Prandini, Antimo Marrazzo, Ivano E. Castelli, Nicolas Mounet, Elsa Passaro, Nicola Marzari

  • Despite the enormous success and popularity of density functional theory, systematic verification and validation studies are still very limited both in number and scope. Here, we propose a universal standard protocol to verify publicly available pseudopotential libraries, based on several independent criteria including verification against all-electron equations of state and plane-wave convergence tests for phonon frequencies, band structure, cohesive energy and pressure. Adopting these criteria we obtain two optimal pseudopotential sets, namely the Standard Solid State Pseudopotential (SSSP) efficiency and precision libraries, tailored for high-throughput materials screening and high-precision materials modelling. As of today, the SSSP precision library is the most accurate open-source pseudopotential library available. This archive entry contains the database of calculations (phonons, cohesive energy, equation of state, band structure, pressure, etc.) together with the ...

Latest version: v7
Publication date: May 21, 2021

Interplay between ferroelectricity and metallicity in BaTiO3


Veronica F. Michel, Tobias Esswein, Nicola A. Spaldin

  • We explore the interplay between ferroelectricity and metallicity, which are generally considered to be contra-indicated properties, in the prototypical ferroelectric barium titanate, BaTiO3. Using first-principles density functional theory, we calculate the effects of electron and hole doping, first by introducing a hypothetical background charge, and second through the introduction of explicit impurities (La, Nb and V for electron doping, and K, Al and Sc for hole doping). We find that, apart from a surprising increase in polarization at small hole concentrations, both charge-carrier types decrease the tendency towards ferroelectricity, with the strength of the polarization suppression, which is different for electrons and holes, determined by the detailed structure of the conduction and valence bands. Doping with impurity atoms increases the complexity and allows us to identify three factors that influence the ferroelectricity: structural effects arising largely from the size ...

Latest version: v1
Publication date: May 21, 2021

Common workflows for computing material properties using different quantum engines


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: v1
Publication date: May 11, 2021

Global free-energy landscapes as a smoothly joined collection of local maps


Federico Giberti, Gareth Tribello, Michele Ceriotti

  • This repository contains the scripts that were used to run the calculations that present a new biasing technique, the Adaptive Topography of Landscape for Accelerated Sampling (ATLAS). The techinque is implemented in plumed-2.0 and the input file are included in the repository, as well as a few scripts to postprocess the calculations and reproduce the plots presented in the paper

Latest version: v1
Publication date: May 08, 2021

Carrier lifetimes and polaronic mass enhancement in the hybrid halide perovskite CH₃NH₃PbI₃ from multiphonon Fröhlich coupling


Martin Schlipf, Samuel Poncé, Feliciano Giustino

  • We elucidate the nature of the electron-phonon interaction in the archetypal hybrid perovskite CH₃NH₃PbI₃ using ab initio many-body calculations and an exactly solvable model. We demonstrate that electrons and holes near the band edges primarily interact with three distinct groups of longitudinal-optical vibrations, in order of importance: the stretching of the Pb-I bond, the bending of the Pb-I-Pb bonds, and the libration of the organic cations. These polar phonons induce ultrafast intraband carrier relaxation over timescales of 6–30 fs and yield polaron effective masses 28% heavier than the bare band masses. These findings allow us to rationalize previous experimental observations and provide a key to understanding carrier dynamics in halide perovskites.

Latest version: v1
Publication date: May 07, 2021

Plasmon energy changes in FeMo14C15B6Erx (x=0-2) bulk metallic glass during in-situ heating


Sengo Kobayashi, James Howe, Mitsuhiro Murayama

  • Variations of volume plasmon energy of both ribbon and bulk FeMo14C15B6Erx (x=0-2) metallic glasses were measured as a function of the temperature in an analytical transmission electron microscope using valence electron energy loss spectroscopy (VEELS). The plasmon energy was found to decrease with increasing temperature, due not only to thermal expansion but also to chemical reordering in the glasses. The chemical reordering stimulates a specific solute cluster formation; M23(C, B)6 solute clusters began to form above about 200°C in both ribbon and bulk FeMo14C15B6Erx (x=0, 0.5, 1) metallic glasses. The formation of the M23(C, B)6 solute clusters was only found above 400°C in the ribbon FeMo14C15B6Er2 metallic glass, indicating inhibition of the M23(C, B)6 solute clusters occurred owing to the formation of Er-(C, B) complexes/clusters. The Er-(C, B) complexes/clusters were formed in the cooling process of the sample fabrication. In contrast to the ribbon sample, the formation of ...

Latest version: v1
Publication date: May 06, 2021

On-the-fly assessment of diffusion barriers of disordered transition metal oxyfluorides using local descriptors


Jin Hyun Chang, Peter Bjørn Jørgensen, Simon Loftager, Arghya Bhowmik, Juan María García Lastra, Tejs Vegge

  • The dataset contains the result of 48 Nudged Elastic Band calculations of Li(2-x)VO2F diffusion barriers in the format of Atomic Simulation Environment (ASE) trajectories. The NEB was performed with VASP, using projector augmented-wave (PAW) method to describe electron-ion interaction. The disordered rock salt cells were created using a 3 x 4 x 4 supercell containing 96 atoms (in case of no vacancies). PBE is used as XC functional while a rotationally invariant Hubbard U correction was applied to the d orbital of V with a U value of 3.25 eV. See more details in the paper.

Latest version: v1
Publication date: May 03, 2021

Finding new crystalline compounds using chemical similarity


Hai-Chen Wang, Silvana Botti, Miguel A. L. Marques

  • We proposed an efficient high-throughput scheme for the discovery of new stable crystalline phases. Our approach was based on the transmutation of known compounds, through the substitution of atoms in the crystal structure with chemically similar ones. The concept of similarity is defined quantitatively using a measure of chemical replaceability, extracted by data mining experimental databases. In this way we build more than 250k possible crystal phases, with almost 20k that are on the convex hull of stability. This dataset contains the optimized structure and the energy of these 250k materials calculated with the PBE approximation, in a format that is convenient for data-mining or for machine-learning applications.

Latest version: v1
Publication date: May 03, 2021

Designing crystallization to tune the performance of phase-change memory: rules of hierarchical melt and coordinate bond


Jin Zhao, Wen-Xiong Song, Tianjiao Xin, Zhitang Song

  • While alloy design has practically shown an efficient strategy to mediate two seemingly conflicted performances of writing speed and data retention in phase-change memory, the detailed kinetic pathway of alloy-tuned crystallization is still unclear. Here, we propose hierarchical melt and coordinate bond strategies to solve them, where the former stabilizes a medium-range crystal-like region and the latter provides a rule to stabilize amorphous. The Er0.52Sb2Te3 compound we designed achieves writing speed of 3.2 ns and ten-year data retention of 161 °C. We provide a direct atomic-level evidence that two neighbor Er atoms stabilize a medium-range crystal-like region, acting as a precursor to accelerate crystallization; meanwhile, the essential reason of stabilization originates from the formation of coordinate bonds by sharing lone-pair electrons of chalcogenide atoms with the empty 5d orbitals of Er atoms. The two rules pave the way for the development of storage-class memory with ...

Latest version: v1
Publication date: Apr 29, 2021

Band gap engineering in blended organic semiconductor films based on dielectric interactions


Katrin Ortstein, Sebastian Hutsch, Mike Hambsch, Kristofer Tvingstedt, Berthold Wegner, Johannes Benduhn, Jonas Kublitski, Martin Schwarze, Sebastian Schellhammer, Felix Talnack, Astrid Vogt, Peter Bäuerle, Norbert Koch, Stefan C. B. Mannsfeld, Hans Kleemann, Frank Ortmann, Karl Leo

  • Blending organic molecules to tune their energy levels is currently investigated as an approach to engineer the bulk and interfacial optoelectronic properties of organic semiconductors. It has been proven that the ionization energy (IE) and electron affinity (EA) can be equally shifted in the same direction by electrostatic effects controlled by blending similar halogenated derivatives with different energetics. Here, we show that the energy gap of organic semiconductors can be tuned by blending as well. We use oligothiophenes with different numbers of thiophene rings as example and investigate their structure and electronic properties. Photoelectron spectroscopy and inverse photoelectron spectroscopy show tunability of the single-particle gap, with the optical gaps showing similar, but smaller effects. Theoretical analysis shows that this tuning is mainly caused by a change in the dielectric constant with blend ratio. Further studies will explore the practical impact of this ...

Latest version: v1
Publication date: Apr 28, 2021

Prediction of yield strength in refractory body-centered-cubic High Entropy Alloys


Francesco Maresca, Chanho Lee, Rui Feng, Yi Chou, Tamas Ungar, Michael Widom, Jonathan Poplawsky, Yi-Chia Chou, Peter Liaw, William Curtin

  • Energy efficiency is motivating the search for new high-temperature metals. Some new body-centered-cubic random multicomponent "high entropy alloys (HEAs)" based on refractory elements (Cr-Mo-Nb-Ta-V-W-Hf-Ti-Zr) possess exceptional strengths at high temperatures but the physical origins of this outstanding behavior are not known. Here, by using a recent mechanistic theory, we have computed the high-temperature (T=1300K) yield strength based on solute strengthening of over 10 million alloys within the whole Al-Cr-Mo-Nb-Ta-V-W-Hf-Ti-Zr alloy family. Also the yield strength/density has been computed. This database enables the efficient search of new alloys with exceptional high-temperature strength.

Latest version: v1
Publication date: Apr 28, 2021

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


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

  • In the record we provide the inputs and outputs for the calculations that support our recent results in the synthesis of pentagon-fused graphene nanoribbons (GNRs). 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 manuscript, 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 ...

Latest version: v1
Publication date: Apr 15, 2021

Rules of formation of H–C–N–O compounds at high pressure and the fates of planetary ices


Lewis J. Conway, Chris J. Pickard, Andreas Hermann

  • Results of an ab initio structure search on the H+C+N+O quaternary space at 500GPa. The solar system’s outer planets, and many of their moons, are dominated by matter from the H–C–N–O chemical space, based on solar system abundances of hydrogen and the planetary ices H2O, CH4 , and NH3 . In the planetary interiors, these ices will experience extreme pressure conditions, around 5 Mbar at the Neptune mantle–core boundary, and it is expected that they undergo phase transitions, decompose, and form entirely new compounds. While temperature will dictate the formation of compounds, ground- state density functional theory allows us to probe the chemical effects resulting from pressure alone. These structural developments in turn determine the planets’ interior structures, thermal evolution, and magnetic field generation, among others. Despite its importance, the H–C–N–O system has not been surveyed systematically to explore which compounds emerge at high-pressure conditions, and what ...

Latest version: v1
Publication date: Apr 12, 2021

Dictionary of 140k GDB and ZINC derived AMONs


Bing Huang, Anatole von Lilienfeld

  • We present all AMONs for GDB and Zinc data-bases using no more than 7 non-hydrogen atoms (AGZ7)---a calculated organic chemistry building-block dictionary based on the AMON approach [Huang and von Lilienfeld, Nature Chemistry (2020)]. AGZ7 records Cartesian coordinates of compositional and constitutional isomers, as well as properties for ∼140k small organic molecules obtained by systematically fragmenting all molecules of Zinc and the majority of GDB17 into smaller entities, saturating with hydrogens, and containing no more than 7 heavy atoms (excluding hydrogen atoms). AGZ7 cover the elements H, B, C, N, O, F, Si, P, S, Cl, Br, Sn and I and includes optimized geometries, total energy and its decomposition, Mulliken atomic charges, dipole moment vectors, quadrupole tensors, electronic spatial extent, eigenvalues of all occupied orbitals, LUMO, gap, isotropic polarizability, harmonic frequencies, reduced masses, force constants, IR intensity, normal coordinates, rotational ...

Latest version: v1
Publication date: Apr 11, 2021

Reinvestigating the surface and bulk electronic properties of Cd3As2


Silvan Roth, Hyungjun Lee, Andrea Sterzi, Michele Zacchigna, Antonio Politano, Raman Sankar, Fang-Cheng Chou, Giovanni Di Santo, Luca Petaccia, Oleg V. Yazyev, Alberto Crepaldi

  • This record contains the experimental results of our reinvestigation of the bulk and surface electronic properties of Cd3As2, a well-known material proposed to realize the 3D Dirac semimetal phase. By using polarization-based matrix element effects in photoemission, we reveal multiple bands crossing the Fermi level, characterized by different orbital character. Those states exhibit also largely different effective masses, and by combining alkali metal deposition and photon energy dependent ARPES, we report that the linearly dispersing band, which was previously interpreted as a bulk Dirac particle, is indeed a 2D surface Dirac state.

Latest version: v1
Publication date: Apr 09, 2021

Showing: 100 of 421 records