References of "Ghosez, Philippe"
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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 detailLattice dynamics of BaTiO3, PbTiO3, and PbZrO3: A comparative first-principles study
Ghosez, Philippe ULg; Cockayne, E.; Waghmare, U. V. et al

in Physical Review. B : Condensed Matter (1999), 60(2), 836-843

The full phonon dispersion relations of lead titanate and lead zirconate in the cubic perovskite structure are computed using first-principles variational density-functional perturbation theory, with nb ... [more ▼]

The full phonon dispersion relations of lead titanate and lead zirconate in the cubic perovskite structure are computed using first-principles variational density-functional perturbation theory, with nb initio pseudopotentials and a plane-wave basis set. Comparison with the results previously obtained for barium titanate shows that the change of a single constituent (Ba to Pb, Ti to Zr) has profound effects on the character and dispersion of unstable modes, with significant implications for the nature of the phase transitions and the dielectric and piezoelectric responses of the compounds. Examination of the interatomic force constants in real space, obtained by a transformation which correctly treats the long-range dipolar contribution, shows that most are strikingly similar, while it is the differences in a few key interactions which produce the observed changes in the phonon dispersions. These trends suggest the possibility of the transferability of force constants to predict the lattice dynamics of perovskite solid solutions. [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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See detailInterplay between the electronic and dynamical properties of barium titanate
Ghosez, Philippe ULg; Gonze, X.; Michenaud, J. P.

in Advanced in Computational Materials Science - II (1998)

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See detailLong-range Coulomb interaction in ZrO2
Detraux, F.; Ghosez, Philippe ULg; Gonze, X.

in Physical Review Letters (1998), 81(15), 3297-3297

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See detailAnomalously large Born effective charges in cubic WO3
Detraux, F.; Ghosez, Philippe ULg; Gonze, X.

in Physical Review. B : Condensed Matter (1997), 56(3), 983-985

Within density-functional theory, we compute the Born effective charges of tungsten trioxyde in its reference cubic phase (defect-perovskite structure). For the tungsten atom, the effective charge tensor ... [more ▼]

Within density-functional theory, we compute the Born effective charges of tungsten trioxyde in its reference cubic phase (defect-perovskite structure). For the tungsten atom, the effective charge tensor is isotropic, with Z(W)*=+12.51. For the oxygen atoms, the two independent components of the tensor, corresponding, respectively, to a displacement of the atom parallel or perpendicular to the W-O bond, have the values Z(O parallel to)* = -9.13 and Z(O perpendicular to)* = -1.68. Z(W)* and Z(O parallel to)* are anomalously large with respect to the nominal ionic charges (+6 on W and -2 on O), but compatible with the Born effective charges found in related ABO(3)-perovskite compounds. [less ▲]

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See detailLong-wavelength behavior of the exchange-correlation kernel in the Kohn-Sham theory of periodic systems
Ghosez, Philippe ULg; Gonze, X.; Godby, R. W.

in Physical Review. B : Condensed Matter (1997), 56(20), 12811-12817

The polarization dependence of the exchange-correlation (re) energy functional of periodic insulators within Kohn-Sham (KS) density-functional theory requires a O(1/q(2)) divergence in the re kernel for ... [more ▼]

The polarization dependence of the exchange-correlation (re) energy functional of periodic insulators within Kohn-Sham (KS) density-functional theory requires a O(1/q(2)) divergence in the re kernel for small vectors q. This behavior, exemplified for a one-dimensional model semiconductor, is also observed when an insulator happens to be described asa KS metal, or vice versa. Although it can occur in the exchange-only kernel, it is not found in the usual local, semilocal, or even nonlocal approximations to KS theory. We also show that the test-charge and. electronic definitions of the macroscopic dielectric constant differ from one another in exact KS theory, but are equivalent in the above-mentioned approximations. [less ▲]

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See detailPolarization dependence of the exchange energy
Gonze, X.; Ghosez, Philippe ULg; Godby, R. W.

in Physical Review Letters (1997), 78(10), 2029-2029

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See detailLattice dynamics and ferroelectric instability of barium titanate
Ghosez, Philippe ULg; Gonze, X.; Michenaud, J. P.

in Ferroelectrics (1997), 194

Using first-principles calculations, we investigate the lattice dynamics of cubic and rhombohedral BaTiO3 and rye discuss the origin of the structural instability of this ferroelectric material. First, we ... [more ▼]

Using first-principles calculations, we investigate the lattice dynamics of cubic and rhombohedral BaTiO3 and rye discuss the origin of the structural instability of this ferroelectric material. First, we report results on the Born effective charges and the dielectric tensor and we emphasize the important reduction of these quantities in the ferroelectric phase, Then, the phonon frequencies at the Gamma point are calculated. We point out the similarity of theoretical eigenvectors in the cubic and rhombohedral phases. We examine the interaction of the vibration modes with the electric field and in particular the giant LO-TO splitting of the ferroelectric mode. Finally, separating the dipole-dipole interaction from the remaining short-range forces, we quantify the balance of forces leading to an unstable phonon in the cubic phase and we demonstrate its sensitivity to tiny effective charge changes. Within our decomposition, the stabilization of the unstable mode in the rhombohedral phase is produced by a reduction of the Born effective charges, while its stabilization under isotropic pressure is associated with a modification of the short-range forces. [less ▲]

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See detailDensity-functional theory of polar insulators
Gonze, X.; Ghosez, Philippe ULg; Godby, R. W.

in Physical Review Letters (1997), 78(2), 294-297

We examine the density-functional theory of macroscopic insulators, obtained in the large-cluster limit or under periodic boundary conditions. For polar crystals, we find that the two procedures are not ... [more ▼]

We examine the density-functional theory of macroscopic insulators, obtained in the large-cluster limit or under periodic boundary conditions. For polar crystals, we find that the two procedures are not equivalent. In a large-cluster case, the exact exchange-correlation potential acquires a homogeneous ''electric field'' which is absent from the usual local approximations, and the Kohn-Sham electronic system becomes metallic. With periodic boundary conditions, such a field ist forbidden, and the polarization deduced from Kohn-Sham wave functions is incorrect even if the exact functional is used. [less ▲]

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See detailRole of the Coulomb interaction on the ferroelectric instability of Barium Titanate
Ghosez, Philippe ULg; Gonze, X.; Michenaud, J. P.

in Ferroelectrics (1996), 186

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See detailCoulomb interaction and ferroelectric instability of BaTiO3
Ghosez, Philippe ULg; Gonze, X.; Michenaud, J. P.

in Europhysics Letters [=EPL] (1996), 33(9), 713-718

Using first-principles calculations, the phonon frequencies at the Gamma-point and the dielectric tensor are determined and analysed for the cubic and rhombohedral phases of BaTiO3. The dipole-dipole ... [more ▼]

Using first-principles calculations, the phonon frequencies at the Gamma-point and the dielectric tensor are determined and analysed for the cubic and rhombohedral phases of BaTiO3. The dipole-dipole interaction is then separated a la Cochran from the remaining short-range forces, in order to investigate their respective influence on lattice dynamics. This analysis highlights the delicate balance of forces leading to an unstable phonon in the cubic phase and demonstrates its extreme sensitivity to effective charge changes. Within our decomposition, the stabilization of the unstable mode in the rhombohedral phase or under isotropic pressure has a different origin. [less ▲]

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See detailA microscopic study of barium titanate
Ghosez, Philippe ULg; Gonze, X.; Michenaud, J. P.

in Ferroelectrics (1995), 164

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See detailSCALING HYPOTHESIS FOR CORRECTIONS TO TOTAL-ENERGY AND STRESS IN PLANE-WAVE-BASED AB-INITIO CALCULATIONS
RIGNANESE, G. M.; Ghosez, Philippe ULg; CHARLIER, J. C. et al

in Physical Review. B : Condensed Matter (1995), 52(11), 8160-8178

We present a technique aimed at preventing plane-wave-based total energy and stress calculations from the effect of abrupt changes in basis set size. This scheme relies on the interpolation of energy as a ... [more ▼]

We present a technique aimed at preventing plane-wave-based total energy and stress calculations from the effect of abrupt changes in basis set size. This scheme relies on the interpolation of energy as a function of the number of plane waves and on a scaling hypothesis that allows us to perform the interpolation for a unique reference volume. From a theoretical point of view, the method is compared to those already proposed in the literature, and its more rigorous derivation is emphasized. From a practical point of view, we illustrate the importance of the correction on different materials (Si, BaTiO3, and He) corresponding to different types of bonding, and to different k-point samplings and cutoff energies. Then, we compare the different approaches for the calculation of a(0), B-0, and B-0' in bulk silicon. [less ▲]

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See detailBORN EFFECTIVE CHARGES OF BARIUM-TITANATE - BAND-BY-BAND DECOMPOSITION AND SENSITIVITY TO STRUCTURAL FEATURES
Ghosez, Philippe ULg; GONZE, X.; LAMBIN, P. et al

in Physical Review. B : Condensed Matter (1995), 51(10), 6765-6768

Detailed reference viewed: 15 (0 ULg)