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See detailImplementation of Density-Functional Perturbation Theory within ABINIT: Proj ector Augmented-Waves and Spin-Orbit
Gonze, X.; Verstraete, Matthieu ULg; Audouze, C. et al

in AIP Conference Proceedings (2012), 1504

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See detailPolarization vortices in germanium telluride nanoplatelets: A theoretical study
Durgun, Engin ULg; Ghosez, Philippe ULg; Shaltaf, R. et al

in Physical Review Letters (2009), 103

Using first-principles calculations based on density functional theory, we study the properties of germanium telluride crystalline nanoplatelets and nanoparticles. Above a diameter of 2.7 nm, we predict ... [more ▼]

Using first-principles calculations based on density functional theory, we study the properties of germanium telluride crystalline nanoplatelets and nanoparticles. Above a diameter of 2.7 nm, we predict the appearance of polarization vortices giving rise to an unusual ferrotoroidic ground state with a spontaneous and reversible toroidal moment of polarization. We highlight the crucial role of inhomogeneous strain in stabilizing polarization vortices. Combined with the phase-change properties of germanium telluride, the ferrotoroidic properties could be of practical interest for ternary logic applications. [less ▲]

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See detailABINIT: First-principles approach to material and nanosystem properties
Gonze, X.; Amadon, B.; Anglade, P.-M. et al

in Computer Physics Communications (2009), 180

ABINIT allows one to study, from first-principles, systems made of lectrons and nuclei (e.g. periodic solids, molecules, nanostructures, etc.), on the basis of Density-Functional Theory (DFT) and many ... [more ▼]

ABINIT allows one to study, from first-principles, systems made of lectrons and nuclei (e.g. periodic solids, molecules, nanostructures, etc.), on the basis of Density-Functional Theory (DFT) and many-Body Perturbation Theory. beyond the computation of the total energy, charge density and electronic structure of such systems, ABINIT also implements many dynamical, dielectric, thermodynamical, mechanical, or electronic properties, at different levels of approximation. The present paper provides an exhustive account of the capabilities of ABINIT. It should be helpful to scienttists that are not familirized with ABINIT, as well as to already regular users. First, we give a broad overview of ABINIT, including the list of the capabilities and how to access them. Then, we present in more details the recent, advance, developments of ABINIT, with adequate references to the underlying theory, as well as the relevant input variables, tests and, if available, ABINIT tutorials. [less ▲]

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See detailDynamical, dielectric, and elastic properties of GeTe investigated with first-principles density functional theory
Shaltaf, R.; Durgun, Engin ULg; Raty, Jean-Yves ULg et al

in Physical Review. B, Condensed Matter and Materials Physics (2008), 78

The dynamical, dielectric, and elastic properties of GeTe, a ferroelectric material in its low-temperature rhombohedral phase, have been investigated using first-principles density functional theory. We ... [more ▼]

The dynamical, dielectric, and elastic properties of GeTe, a ferroelectric material in its low-temperature rhombohedral phase, have been investigated using first-principles density functional theory. We report the electronic energy bands, phonon-dispersion curves, electronic and low-frequency dielectric tensors, infrared reflectivity, Born effective charges, and elastic and piezoelectric tensors and compare them with the existing theoretical and experimental results, as well as with similar quantities available for other ferroelectric materials, when appropriate. [less ▲]

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See detailDensity Functional Perturbation Threory with Spin-Orbit Coupling: the case of Pb
Verstraete, Matthieu ULg; Torrent, M.; Jollet, F. et al

in Physical Review. B : Condensed Matter (2008), 78

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See detailSpecification of an extensible and portable file format for electronic structure and crystallographic data
Gonze, X.; Almbladh, C.-O.; Cucca, A. et al

in Computational Materials Science (2008), 43

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See detailSharing electronic structure and crystallographic data with ETSF_IO
Caliste, D.; Pouillon, Y.; Verstraete, Matthieu ULg et al

in Computer Physics Communications (2008)

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See detailModeling the dissociation and ionization of a sputtered organic molecule
Solomko, V.; Verstraete, Matthieu ULg; Delcorte, A. et al

in Applied Surface Science (2006), 252

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See detailNonlinear optical susceptibilities, Raman efficiencies, and electro-optic tensors from first-principles density functional perturbation theory
Veithen, M.; Gonze, X.; Ghosez, Philippe ULg

in Physical Review. B, Condensed Matter and Materials Physics (2005), 71

The nonlinear response of infinite periodic solids to homogenous electric fields and collective atomic displacements is discussed in the framework of density functional perturbation theory. The approach ... [more ▼]

The nonlinear response of infinite periodic solids to homogenous electric fields and collective atomic displacements is discussed in the framework of density functional perturbation theory. The approach is based on the 2n+1 theorem applied to an electric-field-dependent energy functional. We report the expressions for the calculation of the nonlinear optical susceptibilities, Raman scattering efficiencies, and electro-optic (EO) coefficients. Different formulations of third-order energy derivatives are examined and their convergence with respect to the k-point sampling is discussed. We apply our method to a few simple cases and compare our results to those obtained with distinct techniques. Finally, we discuss the effect of a scissors correction on the EO coefficients and nonlinear optical susceptibilities. [less ▲]

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See detailA brief introduction to the ABINIT software project
Gonze, X.; Rignanese, G.-M.; Verstraete, Matthieu ULg et al

in Zeitschrift für Kristallographie (2005), 220

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See detailFirst-principles study of the electro-optic effect in ferroelectric oxides
Veithen, M.; Gonze, X.; Ghosez, Philippe ULg

in Physical Review Letters (2004), 93

We first present a method to compute the electro-optic tensor from first principles, explicitly taking into account the electronic, ionic and piezoelectric contributions. We then study the nonlinear optic ... [more ▼]

We first present a method to compute the electro-optic tensor from first principles, explicitly taking into account the electronic, ionic and piezoelectric contributions. We then study the nonlinear optic behavior of three paradigmatic ferroelectric oxides. Our calculations reveal the dominant contribution of the soft mode to the electro-optic coefficients in LiNbO3 and BaTiO3 and its minor role in PbTiO3. We identify the coupling between the electric field and the polar atomic displacements along the B-O chains as the origin of the large electro-optic response in perovskite ABO(3) compounds. [less ▲]

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See detailFirst-principles computation of material properties: the ABINIT software project
Gonze, X.; Beuken, J. M.; Caracas, R. et al

in Computational Materials Science (2002), 25(3), 478-492

The density functional theory (DFT) computation of electronic structure, total energy and other properties of materials, is a field in constant progress. In order to stay at the forefront of knowledge, a ... [more ▼]

The density functional theory (DFT) computation of electronic structure, total energy and other properties of materials, is a field in constant progress. In order to stay at the forefront of knowledge, a DFT software project can benefit enormously from widespread collaboration, if handled properly. Also, modern software engineering concepts can considerably ease its development. The ABINIT project relies upon these ideas: freedom of sources, reliability, portability, and self-documentation are emphasised, in the development of a sophisticated plane-wave pseudopotential code. We describe ABINITv3.0, distributed under the GNU General Public License. The list of ABINITv3.0 capabilities is presented, as well as the different software techniques that have been used until now: PERL scripts and CPP directives treat a unique set of FORTRAN90 source files to generate sequential (or parallel) object code for many different platforms; more than 200 automated tests secure existing capabilities; strict coding rules are followed; the documentation is extensive, including online help files, tutorials, and HTML-formatted sources. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailElectron localization: Band-by-band decomposition and application to oxides
Veithen, M.; Gonze, X.; Ghosez, Philippe ULg

in Physical Review. B, Condensed Matter and Materials Physics (2002), 66

Using a plane-wave pseudopotential approach to density functional theory we investigate the electron localization length in various oxides. For this purpose, we first set up a theory of the band-by-band ... [more ▼]

Using a plane-wave pseudopotential approach to density functional theory we investigate the electron localization length in various oxides. For this purpose, we first set up a theory of the band-by-band decomposition of this quantity, more complex than the decomposition of the spontaneous polarization (a related concept), because of the interband coupling. We show its interpretation in terms of Wannier functions and clarify the effect of the pseudopotential approximation. We treat the case of different oxides: BaO, alpha-PbO, BaTiO3, and PbTiO3. We also investigate the variation of the localization tensor during the ferroelectric phase transitions of BaTiO3 as well as its relationship with the Born effective charges. [less ▲]

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See detailSmearing scheme for finite-temperature electronic-structure calculations
Verstraete, Matthieu ULg; Gonze, X.

in Physical Review. B : Condensed Matter (2002), 65

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See detailFirst-principle study of crystals exhibiting an incommensurate phase transition
Gonze, X.; Caracas, R.; Sonnet, R. et al

in AIP Conference Proceedings (2000), 535

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See detailFirst Principles Study of the lattice instabilities in BaxSr1-xTiO3
Ghosez, Philippe ULg; Desquesnes, D.; Gonze, X. et al

in AIP Conference Proceedings (2000), 535

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See detailBand-by-band decompositions of the Born effective charges
Ghosez, Philippe ULg; Gonze, X.

in Journal of Physics : Condensed Matter (2000), 12(43), 9179-9188

The Born effective charge, Z*, that describes the polarization created by collective atomic displacements, can be computed from first principles following different techniques. We establish the ... [more ▼]

The Born effective charge, Z*, that describes the polarization created by collective atomic displacements, can be computed from first principles following different techniques. We establish the connections existing between these different formulations, and analyse the related band-by-band decompositions. We show that unlike for the full Z*, the different band-by-band values are not equal, and emphasize that one of them has a natural physical meaning in terms of Wannier functions. [less ▲]

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See detailFirst-principles characterization of the four phases of barium titanate
Ghosez, Philippe ULg; Gonze, X.; Michenaud, J. P.

in Ferroelectrics (1999), 220(1-2), 1-15

Using a first-principles approach, the four phases of perovskite barium titanate are studied. We determine the lattice parameter, the bulk modulus and the cohesive energy of the cubic phase; the relaxed ... [more ▼]

Using a first-principles approach, the four phases of perovskite barium titanate are studied. We determine the lattice parameter, the bulk modulus and the cohesive energy of the cubic phase; the relaxed atomic positions in the three ferroelectric structures; and the evolution of the electronic properties from one phase to the other. The role of electronic exchange-correlation energy in the stabilization of the different phases is also investigated. [less ▲]

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See detailAb initio phonon dispersion curves and interatomic force constants of barium titanate
Ghosez, Philippe ULg; Gonze, X.; Michenaud, J. P.

in Ferroelectrics (1998), 206(1-4), 205-217

The phonon dispersion curves of cubic BaTiO3 have been computed within a first-principles approach and the results compared to the experimental data. The curves obtained are very similar to those reported ... [more ▼]

The phonon dispersion curves of cubic BaTiO3 have been computed within a first-principles approach and the results compared to the experimental data. The curves obtained are very similar to those reported for KNbO3 by Yu and Krakauer (Phys. Rev. Lett., 74, 4067 (1995)). They reveal that correlated atomic displacements along [100] chains are at the origin of the ferroelectric instability. A simplified model illustrates that spontaneous collective displacements will occur when a dozen of aligned atoms are coupled. The longitudinal interatomic force constant between nearest neighbour Ti and O atoms is relatively weak in comparison to that between Ti atoms in adjacent cells. The small coupling between Ti and O displacements seems however necessary to reproduce a linear ferroelectric instability. [less ▲]

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See detailDynamical atomic charges: The case of ABO(3) compounds
Ghosez, Philippe ULg; Michenaud, J. P.; Gonze, X.

in Physical Review. B : Condensed Matter (1998), 58(10), 6224-6240

Based on recent first-principles computations in perovskite compounds, especially BaTiO3, we examine the significance of the Born effective charge concept and contrast it with other atomic charge ... [more ▼]

Based on recent first-principles computations in perovskite compounds, especially BaTiO3, we examine the significance of the Born effective charge concept and contrast it with other atomic charge definitions, either static (Mulliken, Bader, etc.) or dynamical (Callen, Szigeti, etc.). It is shown that static and dynamical charges are not driven by the same underlying parameters. A unified treatment of dynamical charges in periodic solids and large clusters is proposed. The origin of the difference between static and dynamical charges is discussed in terms of local polarizability and delocalized transfers of charge: local models succeed in reproducing anomalous effective charges thanks to large atomic polarizabilities but, in ABO(3) compounds, ab initio calculations favor the physical picture based upon transfer of charges. Various results concerning barium and strontium titanates are presented. The origin of anomalous Born effective charges is discussed thanks to a band-by-band decomposition which allows us to identify the displacement of the Wannier center of separated bands induced by an atomic displacement. The sensitivity of the Born effective charges to microscopic and macroscopic strains is examined. Finally, we estimate the spontaneous polarization in the four phases of barium titanate. [less ▲]

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