Data and post-processing scripts for npj Quantum Materials 4:5, 2019
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Energetics of the coupled electronic–structural transition in the rare-earth
nickelates
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https://rdcu.be/bkZle / https://doi.org/10.1038/s41535-019-0145-4
A. Hampel, P. Lio, C. Franchini & C. Ederer

The comressed tgz archive contains jupyter notebooks (https://jupyter.org/) that
will read the data produced by VASP and the triqs DMFT framework
(https://triqs.github.io/triqs/2.1.x/) and post-process it to the figures found
in our publication. All input and output data is contained in the archive:
approximately 23GB uncompressed data files from ~1400 calculations. The jupyter
notebooks should explain the directory structure sufficiently and allow the
reader to follow our post-processing workflows. The important output files for
the DFT+DMFT calculations are called "observables_imp#.dat", which are read by
the jupyter notebooks. To reproduce the calculations, all input files are
included as well, and one can use our public DFT+DMFT code on
https://github.com/materialstheory/soliDMFT as used for the publication.

Note: Due to license reasons we had to remove all VASP POTCAR files. Please have
a look in the corresponding OUTCAR for information which POTCAR to use.

notebooks:
- cRPA-eg-eg.ipynb: cRPA calculations and extraction of Hubbard-Kanamori parameters
- csc-dmft-nickelate-energetics.ipynb: DFT+DMFT energetics for Lu, Sm, Pr
- csc-energetics-Lu-reduced-rots.ipynb: DFT+DMFT energetics for Lu with reduced rotations
- csc-dmft-phase-diagrams.ipynb: DFT+DMFT U,J phase diagrams for Pr and Lu

original abstract of the publication:
Rare-earth nickelates exhibit a metal–insulator transition accompanied by a
structural distortion that breaks the symmetry between formerly equivalent Ni
sites. The quantitative theoretical description of this coupled
electronic–structural instability is extremely challenging. Here, we address
this issue by simultaneously taking into account both structural and electronic
degrees of freedom using a charge self-consistent combination of density
functional theory and dynamical mean-field theory, together with screened
interaction parameters obtained from the constrained random phase approximation.
Our total energy calculations show that the coupling to an electronic
instability toward a charge disproportionated insulating state is crucial to
stabilize the structural distortion, leading to a clear first order character of
the coupled transition. The decreasing octahedral rotations across the series
suppress this electronic instability and simultaneously increase the screening
of the effective Coulomb interaction, thus weakening the correlation effects
responsible for the metal–insulator transition. Our approach allows to obtain
accurate values for the structural distortion and thus facilitates a
comprehensive understanding, both qualitatively and quantitatively, of the
complex interplay between structural properties and electronic correlation
effects across the nickelate series.