Electronic interaction UppU_{pp} on oxygen pp orbitals in oxides: Role of correlated orbitals on the example of UO2_2 and TiO2_2

We carry out a detailed study of the role of electronic interaction on $p$ oxygen orbitals in a Mott insulator oxide (UO$_2$) and a charge transfer oxide (TiO$_2$). First, we calculate values of effective interactions \Uff, \Upp{} and $U_{fp}$ in UO$_2$ and \Udd{}, \Upp{} and $U_{dp}$ in TiO$_2$. Second, we analyze the role of electronic interactions \Upp{} on $p$ orbitals of oxygen in spectral and structural properties. Finally, we show that this role depends strongly on the definition of correlated orbitals and that using Wannier functions leads to more physical results for spectral and structural properties

Mechanism for the {\alpha} -> {\epsilon} phase transition in iron

The mechanism of the {\alpha}-{\epsilon} transition in iron is reconsidered. A path in the Burgers description of the bcc/hcp transition different from those previously considered is proposed. It relies on the assumption that shear and shuffle are decoupled and requires some peculiar magnetic order, different from that of {\alpha} and {\epsilon} phases as found in Density-Functional Theory. Finally, we put forward an original mechanism for this transition, based on successive shuffle motion of layers, which is akin to a nucleation-propagation process rather than to some uniform motion.Comment: 6 pages, 5 figure

Study of the volume and spin collapse in orthoferrite LuFeO_3 using LDA+U

Rare earth (R) orthoferrites RFeO_3 exhibit large volume transitions associated with a spin collapse. We present here ab initio calculations on LuFeO_3. We show that taking into account the strong correlation among the Fe-3d electrons is necessary. Indeed, with the LDA+U method in the Projector Augmented Wave (PAW), we are able to describe the isostructural phase transition at 50 GPa, as well as a volume discontinuity of 6.0% at the transition and the considerable reduction of the magnetic moment on the Fe ions. We further investigate the effect of the variation of U and J and find a linear dependence of the transition pressure on these parameters. We give an interpretation for the non-intuitive effect of J. This emphasizes the need for a correct determination of these parameters especially when the LDA+U is applied to systems (e.g in geophysical investigations) where the transition pressure is a priori unknown

ABINIT: Overview and focus on selected capabilities

Paper published as part of the special topic on Electronic Structure SoftwareABINIT is probably the first electronic-structure package to have been released under an open-source license about 20 years ago. It implements density functional theory, density-functional perturbation theory (DFPT), many-body perturbation theory (GW approximation and Bethe–Salpeter equation), and more specific or advanced formalisms, such as dynamical mean-field theory (DMFT) and the “temperaturedependent effective potential” approach for anharmonic effects. Relying on planewaves for the representation of wavefunctions, density, and other space-dependent quantities, with pseudopotentials or projector-augmented waves (PAWs), it is well suited for the study of periodic materials, although nanostructures and molecules can be treated with the supercell technique. The present article starts with a brief description of the project, a summary of the theories upon which ABINIT relies, and a list of the associated capabilities. It then focuses on selected capabilities that might not be present in the majority of electronic structure packages either among planewave codes or, in general, treatment of strongly correlated materials using DMFT; materials under finite electric fields; properties at nuclei (electric field gradient, Mössbauer shifts, and orbital magnetization); positron annihilation; Raman intensities and electro-optic effect; and DFPT calculations of response to strain perturbation (elastic constants and piezoelectricity), spatial dispersion (flexoelectricity), electronic mobility, temperature dependence of the gap, and spin-magnetic-field perturbation. The ABINIT DFPT implementation is very general, including systems with van der Waals interaction or with noncollinear magnetism. Community projects are also described: generation of pseudopotential and PAW datasets, high-throughput calculations (databases of phonon band structure, second-harmonic generation, and GW computations of bandgaps), and the library LIBPAW. ABINIT has strong links with many other software projects that are briefly mentioned.This work (A.H.R.) was supported by the DMREF-NSF Grant No. 1434897, National Science Foundation OAC-1740111, and U.S. Department of Energy DE-SC0016176 and DE-SC0019491 projects. N.A.P. and M.J.V. gratefully acknowledge funding from the Belgian Fonds National de la Recherche Scientifique (FNRS) under Grant No. PDR T.1077.15-1/7. M.J.V. also acknowledges a sabbatical “OUT” grant at ICN2 Barcelona as well as ULiège and the Communauté Française de Belgique (Grant No. ARC AIMED G.A. 15/19-09). X.G. and M.J.V. acknowledge funding from the FNRS under Grant No. T.0103.19-ALPS. X.G. and G.-M. R. acknowledge support from the Communauté française de Belgique through the SURFASCOPE Project (No. ARC 19/24-057). X.G. acknowledges the hospitality of the CEA DAM-DIF during the year 2017. G.H. acknowledges support from the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under Contract No. DE-AC02-05-CH11231 (Materials Project Program No. KC23MP). The Belgian authors acknowledge computational resources from supercomputing facilities of the University of Liège, the Consortium des Equipements de Calcul Intensif (Grant No. FRS-FNRS G.A. 2.5020.11), and Zenobe/CENAERO funded by the Walloon Region under Grant No. G.A. 1117545. M.C. and O.G. acknowledge support from the Fonds de Recherche du Québec Nature et Technologie (FRQ-NT), Canada, and the Natural Sciences and Engineering Research Council of Canada (NSERC) under Grant No. RGPIN-2016-06666. The implementation of the libpaw library (M.T., T.R., and D.C.) was supported by the ANR NEWCASTLE project (Grant No. ANR-2010-COSI-005-01) of the French National Research Agency. M.R. and M.S. acknowledge funding from Ministerio de Economia, Industria y Competitividad (MINECO-Spain) (Grants Nos. MAT2016-77100-C2-2-P and SEV-2015-0496) and Generalitat de Catalunya (Grant No. 2017 SGR1506). This work has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation program (Grant Agreement No. 724529). P.G. acknowledges support from FNRS Belgium through PDR (Grant No. HiT4FiT), ULiège and the Communauté française de Belgique through the ARC project AIMED, the EU and FNRS through M.ERA.NET project SIOX, and the European Funds for Regional Developments (FEDER) and the Walloon Region in the framework of the operational program “Wallonie-2020.EU” through the project Multifunctional thin films/LoCoTED. The Flatiron Institute is a division of the Simons Foundation. A large part of the data presented in this paper is available directly from the Abinit Web page www.abinit.org. Any other data not appearing in this web page can be provided by the corresponding author upon reasonable request.Peer reviewe

ETUDE THEORIQUE DE LA COHESION ET DE L'ECRANTAGE DANS LES SEMICONDUCTEURS ET LES ISOLANTS

NOUS AVONS ETUDIE EN THEORIE DE LA FONCTIONNELLE DE LA DENSITE (DFT) DANS L'APPROXIMATION LDA, DIVERS COMPOSES DU SYSTEME SICN, DONT L'ETUDE EXPERIMENTALE EST EN EXPANSION. NOUS AVONS CONFIRME LES CARACTERISATIONS STRUCTURALES DU COMPOSE RECEMMENT SYNTHETISE SI 2CN 4 ET MONTRE QUE PAR RAPPORT A D'AUTRES COMPOSES CONTENANT DES LIAISONS CN, SON MODULE DE COMPRESSIBILITE EST FAIBLE. AUSSI IL POURRAIT ETRE UTILISE COMME UN PRECURSEUR INTERESSANT POUR LA SYNTHESE DE NANOCOMPOSITES. NOUS APPUYONS CETTE IDEE GRACE A UNE ANALYSE DE SA STABILITE, EN ACCORD AVEC LES DONNEES EXPERIMENTALES. DE PLUS, EN CE QUI CONCERNE L'INSERTION DE QUELQUES DEFAUTS DE CARBONE C S I DANS SI 3N 4, NOUS MONTRONS QU'ELLE CONDUIT A UNE DESTABILISATION ENERGETIQUE ET QU'UN FORT TAUX DE DEFAUT EST NECESSAIRE POUR RELAXER LES CONTRAINTES. CETTE ETUDE PEUT EN OUTRE PERMETTRE DE CONSTRUIRE UN POTENTIEL EMPIRIQUE D'INTERACTION DANS LE SYSTEME SI/C/N. SI LES PROPRIETES D'ETAT FONDAMENTAL DES SOLIDES SONT BIEN DECRITES DANS LE CADRE DE LA DFT-LDA, LE CALCUL DES ENERGIES DE QUASIPARTICULES POSE DES PROBLEMES FONDAMENTAUX. UNE METHODE GW UTILISANT UN MODELE D'ECRANTAGE (VALIDE POUR DES SEMICONDUCTEURS) LES CONTOURNE MAIS CONDUIT NEANMOINS, DANS LE CAS DE SRTIO 3, A UNE SURESTIMATION DU GAP. NOUS AVONS ALORS ENTREPRIS UNE ETUDE APPROFONDIE DES EFFETS D'ECRANTAGE EN DFT-LDA DANS LES SEMICONDUCTEURS ET LES ISOLANTS. DANS CES DERNIERS, NOUS METTONS EN EVIDENCE L'IMPORTANCE ET LA SPECIFICITE DES EFFETS D'ECRANTAGE DUS A L'INHOMOGENEITE DE LA DENSITE. POUR LES REPRODUIRE, NOUS PROPOSONS ET VALIDONS ALORS UNE METHODE DE CALCUL DE LA FONCTION DIELECTRIQUE SUFFISAMMENT LEGERE POUR ETRE UTILISEE POUR CALCULER LES ENERGIES DE QUASIPARTICULES DANS DES SYSTEMES PLUS COMPLEXES. EN OUTRE, NOUS AVONS EVALUE LA PRECISION DES MODELES SIMPLES DE FONCTION DIELECTRIQUE ET FORMULE UNE PROCEDURE POUR LES AMELIORER.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Screened Coulomb interaction calculations: cRPA implementation and applications to dynamical screening and self-consistency in uranium dioxide and cerium

see also Erratum Phys. Rev. B 96, 199907 (2017) - https://journals.aps.org/prb/abstract/10.1103/PhysRevB.96.199907International audienceWe report an implementation of the constrained Random Phase Approximation (cRPA) method within the Projector Augmented-Wave framework. It allows for the calculation of the screened interaction in the same Wannier orbitals as our recent DFT+$U$ and DFT+DMFT implementations. We present calculations of the dynamical Coulomb screened interaction in uranium dioxide and $\alpha$ and $\gamma$ cerium on Wannier functions. We show that a self-consistent calculation of the static screened interaction in DFT+$U$ together with a consistent Wannier basis is mandatory for $\gamma$ cerium and uranium dioxide. We emphasize that a static approximation for the screened interaction in $\alpha$ cerium is too drastic

DFT+ U study of self-trapping, trapping, and mobility of oxygen-type hole polarons in barium stannate

International audienceThe charge-transfer insulating perovskite oxides currently used as fuel cell electrolytes undergo, at high temperature, an oxidation reaction 1 2 O 2 (g) + V • • O → O X O + 2h • , that produces oxygen-type holes. Understanding the nature and mobility of these oxygen-type holes is an important step to improve the performance of devices, but presents a theoretical challenge since, in their localized form, they cannot be captured by standard density functional theory. Here, we employ the DFT+U formalism with a Hubbard correction on the p orbitals of oxygen to investigate several properties of these holes, in the particular case of BaSnO 3. We describe the small oxygen-type hole polarons, the self-trapping at their origin, and their trapping by trivalent dopants (Ga, Sc, In, Lu, Y, Gd, La). Strong similarities with protonic defects are observed concerning the evolution of the trapping energy with ionic radius of the dopant. Moreover, we show that long-range diffusion of holes is a complex phenomenon, that proceeds by a succession of several mechanisms. However, the standard implementation of DFT+U within the projector augmented-wave (PAW) formalism leads to use very large, unphysical values of U for the O-p orbital. We propose here a slightly modified DFT+U scheme, that takes into account the fact that the O-p is truncated in usual DFT+U implementation in PAW. This scheme yields more physical values of U than the ones traditionally used in the literature, and describes well the properties of the hole polaron

Facilities and practices for linear response Hubbard parameters U and J in Abinit

International audienceMembers of the DFT+U family of functionals are increasingly prevalent methods of addressing errors intrinsic to (semi-) local exchange-correlation functionals at minimum computational cost, but require their parameters U and J to be calculated in situ for a given system of interest, simulation scheme, and runtime parameters. The SCF linear response approach offers ab initio acquisition of the U and has recently been extended to compute the J analogously, which measures localized errors related to exchange-like effects. We introduce a renovated post-processor, the lrUJ utility, together with this detailed best-practices guide, to enable users of the popular, open-source Abinit first-principles simulation suite to engage easily with in situ Hubbard parameters and streamline their incorporation into material simulations of interest. Features of this utility, which may also interest users and developers of other DFT codes, include $n$-degree polynomial regression, error analysis, Python plotting facilities, didactic documentation, and avenues for further developments. In this technical introduction and guide, we place particular emphasis on the intricacies and potential pitfalls introduced by the projector augmented wave (PAW) method, SCF mixing schemes, and non-linear response, several of which are translatable to DFT+U(+J) implementations in other packages