References of "Ghosez, Philippe"
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See detailEngineering Multiferroism in CaMnO3
Bhattacharjee, Satadeep; Bousquet, Eric ULg; Ghosez, Philippe ULg

in Physical Review Letters (2009), 102

Structural instabilities of CaMnO3 are investigated from first principles. We point out that, on top of a strong antiferrodistortive instability responsible for its orthorhombic ground state, the cubic ... [more ▼]

Structural instabilities of CaMnO3 are investigated from first principles. We point out that, on top of a strong antiferrodistortive instability responsible for its orthorhombic ground state, the cubic perovskite structure of CaMnO3 also exhibits a weak ferroelectric instability. Although ferroelectricity is suppressed by antiferrodistortive motions, we show that it can be favored using strain or chemical engineering in order to make CaMnO3 multiferroic. We finally highlight that the ferroelectric instability of CaMnO3 is Mn-dominated. This illustrates that, contrary to common belief, ferroelectricity and magnetism are not necessarily exclusive but can be driven by the same cation. [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 detailCorrelation between optical constants and crystal chemical parameters of ZrW2O8
Shannon, Robert D; Fischer, Reinhard X; Medenbach, Olaf et al

in Journal of Solid State Chemistry (2009), 182(10), 2762-2768

The refractive indices of ZrW2O8, measured at wavelengths of 435.8-643.8 nm, were used to calculate n(D) at lambda = 589.3 nm and n(infinity) at lambda = infinity from a one-term Sellmeier equation ... [more ▼]

The refractive indices of ZrW2O8, measured at wavelengths of 435.8-643.8 nm, were used to calculate n(D) at lambda = 589.3 nm and n(infinity) at lambda = infinity from a one-term Sellmeier equation. Refractive indices, n(D) and dispersion values, A, are, respectively, 1.8794 and 114 x 10(-16) m(2). The high dispersion, relative to other molybdates, tungstates and Zr-containing compounds, is attributed to the low value of E-o = 7.7 eV and mean cation coordination number. Total electronic polarizabilities, alpha(total), were calculated from n(infinity) and the Lorenz-Lorentz equation. The unusually large difference between the observed polarizability of 20.087 angstrom(3) and the calculated total polarizability alpha(T) of 17.59 angstrom(3) (Delta = +12.4%) is attributed to (1) a large M-O-W angle, (2) a high degree of W 5d-O(terminal) 2p and Zr nd-O 2p hybridization, and (3) unusually high oxygen displacement factors, B(O), normalized to B(W). (C) 2009 Elsevier Inc. All rights reserved. [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 detailA new hybrid exchange-correlation functional for accurate prediction of the electronic and structural properties of ferroelectric oxides
Bilc, Daniel ULg; Orlando, R.; Shaltaf, R. et al

in Physical Review. B, Condensed Matter and Materials Physics (2008), 77

Using a linear combination of atomic orbitals approach, we report a systematic comparison of various density functional theory (DFT) and hybrid exchange-correlation functionals for the prediction of the ... [more ▼]

Using a linear combination of atomic orbitals approach, we report a systematic comparison of various density functional theory (DFT) and hybrid exchange-correlation functionals for the prediction of the electronic and structural properties of prototypical ferroelectric oxides. It is found that none of the available functionals is able to provide, at the same time, accurate electronic and structural properties of the cubic and tetragonal phases of BaTiO3 and PbTiO3. Some, although not all, usual DFT functionals predict the structure with acceptable accuracy, but always underestimate the electronic band gaps. Conversely, common hybrid functionals yield an improved description of the band gaps, but overestimate the volume and atomic distortions associated with ferroelectricity, giving rise to an unacceptably large c/a ratio for the tetragonal phases of both compounds. This supertetragonality is found to be induced mainly by the exchange energy corresponding to the generalized gradient approximation (GGA) and, to a lesser extent, by the exact exchange term of the hybrid functional. We thus propose an alternative functional that mixes exact exchange with the recently proposed GGA of Wu and Cohen [Phys. Rev. B 73, 235116 (2006)] which, for solids, improves over the treatment of exchange of the most usual GGA's. The new functional renders an accurate description of both the structural and electronic properties of typical ferroelectric oxides. [less ▲]

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See detailFirst-principles study of the dielectric and dynamical properties of orthorhombic CaMnO3
Bhattacharjee, Satadeep; Bousquet, Eric ULg; Ghosez, Philippe ULg

in Journal of Physics : Condensed Matter (2008), 20

The structural, dielectric and dynamical properties of the low temperature antiferromagnetic orthorhombic phase of CaMnO3 have been computed from first principles, using a density functional theory ... [more ▼]

The structural, dielectric and dynamical properties of the low temperature antiferromagnetic orthorhombic phase of CaMnO3 have been computed from first principles, using a density functional theory approach within the local spin density approximation. The theoretical structural parameters are in good agreement with experiment. The full set of zone-center phonons is reported, allowing new assignment of experimental Raman data and providing reference values for the interpretation of future infrared phonon measurements. It is shown that the static dielectric constant is very large and comparable in amplitude to that of isostructural CaTiO3. In contrast to the pseudocubic structure, it is also highly anisotropic. These features are discussed in relationship to the anomalous Born effective charges and the presence of low frequency polar modes. [less ▲]

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See detailNew insight into the concept of ferroelectric correlation volume
Geneste, Gregory; Bousquet, Eric ULg; Ghosez, Philippe ULg

in Journal Of Computational And Theoretical Nanoscience (2008), 5(4), 517-520

Using an effective Hamiltonian derived from first-principles calculations, we discuss the concept of "ferroelectric correlation volume" and show that it cannot be uniquely defined: it is not the size but ... [more ▼]

Using an effective Hamiltonian derived from first-principles calculations, we discuss the concept of "ferroelectric correlation volume" and show that it cannot be uniquely defined: it is not the size but the anisotropic shape of the polar region that is crucial for stabilizing a ferroelectric distortion into a ferroelectric materials. To provide basic understanding of this result, the stability of a polar region is analyzed in term of intra-chain and inter-chain interactions. [less ▲]

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See detailFirst-Principles Study of Ferroelectric Oxide Epitaxial Thin Films and Superlattices: Role of the Mechanical and Electrical Boundary Conditions
Junquera, Javier; Ghosez, Philippe ULg

in Journal Of Computational And Theoretical Nanoscience (2008), 5(11), 2071-2088

In this review, we propose a summary of the most recent advances in the first-principles study of ferroelectric oxide epitaxial thin films and multilayers. We discuss in detail the key roles of mechanical ... [more ▼]

In this review, we propose a summary of the most recent advances in the first-principles study of ferroelectric oxide epitaxial thin films and multilayers. We discuss in detail the key roles of mechanical and electrical boundary conditions, providing to the reader the basic background for a simple and intuitive understanding of the evolution of the ferroelectric properties in many nanostructures. Going further we also highlight promising new avenues and future challenges within this exciting field or researches. [less ▲]

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See detailImproper ferroelectricity in perovskite oxide artificial superlattices
Bousquet, Eric ULg; Dawber, Matthew; Stucki, Nicolas et al

in Nature (2008), 452(7188), 732-736

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See detailFirst-principles calculations of the nonlinear optical susceptibilities and Raman scattering spectra of lithium niobate
Hermet, P.; Veithen, M.; Ghosez, Philippe ULg

in Journal of Physics : Condensed Matter (2007), 19

Nonlinear optical susceptibilities and nonresonant Raman scattering spectra of the ferroelectric phase of lithium niobate (LiNbO3) are computed using a first-principles approach based on density ... [more ▼]

Nonlinear optical susceptibilities and nonresonant Raman scattering spectra of the ferroelectric phase of lithium niobate (LiNbO3) are computed using a first-principles approach based on density functional theory and taking advantage of a recent implementation based on the nonlinear response formalism and the 2n+1 theorem. Infrared reflectivity spectra of the ferroelectric phase of LiNbO3 are also calculated. New assignments are proposed for the E-modes, clarifying a longstanding debate in the literature. In addition, it is shown that knowledge of the nonlinear optical susceptibility tensor of LiNbO3 does not significantly alter the profile of its Raman spectra in a configuration where the longitudinal optic modes are involved. [less ▲]

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See detailTailoring the properties of artificially layered ferroelectric superlattices
Dawber, Matthew; Stucki, Nicolas; Lichtensteiger, Celine et al

in Advanced Materials (2007), 49(23), 4153-4159

The polarization of PbTiO3/SrTiO3 superlattices is experimentally tuned from 0-60 mu C/cm(-2) and the transition temperature from room temperature to 1000 K while maintaining a perfect crystal structure ... [more ▼]

The polarization of PbTiO3/SrTiO3 superlattices is experimentally tuned from 0-60 mu C/cm(-2) and the transition temperature from room temperature to 1000 K while maintaining a perfect crystal structure and low leakage currents (see figure). A simple model based on Landau theory is developed as a guide for the straightforward production of samples with ferroelectric properties designed for particular applications. [less ▲]

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See detailRaman and infrared spectra of multiferroic bismuth ferrite from first principles
Hermet, Patrick ULg; Goffinet, Marco ULg; Kreisel, J. et al

in Physical Review. B, Condensed Matter and Materials Physics (2007), 75

The entire zone-center phonon spectrum of the R3c ferroelectric antiferromagnetic phase of bismuth ferrite is computed using a first-principles approach based on density functional theory. Two phonon ... [more ▼]

The entire zone-center phonon spectrum of the R3c ferroelectric antiferromagnetic phase of bismuth ferrite is computed using a first-principles approach based on density functional theory. Two phonon modes exhibiting eigendisplacement vectors that strongly overlap with the atomic distortions taking place at the ferroelectric structural phase transition are identified and give support to a transition with displacive character. Both Raman and infrared reflectivity spectra are also computed, providing benchmark theoretical results for the assignment of experimental spectra. [less ▲]

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See detailFirst-principles study of filled and unfilled antimony skutterudites
Ghosez, Philippe ULg; Veithen, Marek

in Journal of Physics : Condensed Matter (2007), 19

Using a first-principles approach based on density-functional theory, the electronic, dielectric and dynamical properties of the skutterudites CoSb3 and TlFeCo3Sb12 are studied. In particular, the ... [more ▼]

Using a first-principles approach based on density-functional theory, the electronic, dielectric and dynamical properties of the skutterudites CoSb3 and TlFeCo3Sb12 are studied. In particular, the electron localization tensor, static and dynamic effective charges, static and optical dielectric constants and phonon dispersion curves are computed. The Born effective charges are found to be significantly larger than the static charges of the ions. Moreover, the static dielectric constant of TlFeCo3Sb12 is found to be significantly larger than that of CoSb3. The analysis of the phonon dispersion curves reveals a low-energy mode due to coupled vibrations of Tl and Sb. This mode is at the origin of a well-defined peak in the phonon density of states of TlFeCo3Sb12 and its mode effective charge is related to the increase of the dielectric constant in TlFeCo3Sb12. Our results are compared to recent experiments performed on CoSb3 and TlFeCo3Sb12, and differences between the lattice dynamics of TlFeCo3Sb12 and other filled skutterudites are highlighted. [less ▲]

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See detailFirst-principles studies of ferroelectric oxides
Rabe, K. M.; Ghosez, Philippe ULg

in Physics of Ferroelectrics: A Modern Perspective (2007)

The application of first-principles methods to the study of ferroelectric oxides is reviewed. While the main focus is on the perovskites, particularly the most-studied compounds BaTiO3, PbTiO3, and SrTiO3 ... [more ▼]

The application of first-principles methods to the study of ferroelectric oxides is reviewed. While the main focus is on the perovskites, particularly the most-studied compounds BaTiO3, PbTiO3, and SrTiO3, other oxide families, including LiNbO3, layered perovskites, nitrites and nitrates, and electronic and magnetic ferroelectrics, are included. Results are presented for crystal structure, polarization and dielectric and piezoelectric coefficients. The identification of lattice instabilities through the computation of phonon dispersion relations for a high-symmetry reference phase is presented. Results at nonzero temperature, obtained through effective Hamiltonian and interatomic potential approaches, are given. Calculations for solid solutions, defects, thin films, superlattices and nanostructures are described. Challenges and prospects for future research are identified. [less ▲]

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See detailRaman scattering in crystalline oligothiophenes: A comparison between density functional theory and bond polarizability model
Hermet, P.; Izard, N.; Rahmani, A. et al

in Journal of Physical Chemistry B (2006), 110(49), 24869-24875

Raman intensity of intramolecular and lattice modes of crystalline alpha-bithiophene (alpha-2T) are investigated within density functional theory using a nonlinear response formalism. First, comparison ... [more ▼]

Raman intensity of intramolecular and lattice modes of crystalline alpha-bithiophene (alpha-2T) are investigated within density functional theory using a nonlinear response formalism. First, comparison between the calculated Raman spectrum and the experimental data allows the assignment of the main Raman lines over the whole frequency range. Then, a bond polarizability (BP) model, limited to first neighbors, is built. We show that, although the BP model cannot reproduce the changes of dielectric susceptibility under individual atomic displacements, it is accurate enough to reproduce the profile of the unpolarized nonresonant Raman spectrum of alpha-2T powder. Finally, the BP model, fitted on our first-principles results on alpha-2T, is applied with success to the alpha-quaterthiophene polymorph phases and alpha-sexithiophene, demonstrating on practical examples that first-principles and BP approaches are powerful complementary tools to calculate the nonresonant Raman spectrum of alpha-2T and make reasonable predictions on larger oligothiophenes. [less ▲]

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See detailFirst-principles study of barium titanate under hydrostatic pressure
Bousquet, Eric ULg; Ghosez, Philippe ULg

in Physical Review. B, Condensed Matter and Materials Physics (2006), 74

The behavior of the ferroelectric instability of cubic barium titanate under increasing hydrostatic pressure is investigated from first principles. Beyond a rapid suppression and then reappearance of this ... [more ▼]

The behavior of the ferroelectric instability of cubic barium titanate under increasing hydrostatic pressure is investigated from first principles. Beyond a rapid suppression and then reappearance of this instability at about 140 GPa, we highlight a sudden change in the dynamical behavior of BaTiO3 at a pressure of approximate to 20 GPa. We show that the ferroelectric instability at high pressure has a totally different character than at atmospheric pressure. From the analysis of the interatomic force constants, we demonstrate that the destabilizing role of the short-range forces at high pressure must be related to the change of the soft mode eigenvector rather than to an original electronic effect. [less ▲]

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See detailScaling of structure and electrical properties in ultrathin epitaxial ferroelectric heterostructures
Nagarajan, V.; Junquera, J.; He, J. Q. et al

in Journal of Applied Physics (2006), 100

Scaling of the structural order parameter, polarization, and electrical properties was investigated in model ultrathin epitaxial SrRuO3/PbZr0.2Ti0.8O3/SrRuO3/SrTiO3 heterostructures. High-resolution ... [more ▼]

Scaling of the structural order parameter, polarization, and electrical properties was investigated in model ultrathin epitaxial SrRuO3/PbZr0.2Ti0.8O3/SrRuO3/SrTiO3 heterostructures. High-resolution transmission electron microscopy images revealed the interfaces to be sharp and fully coherent. Synchrotron x-ray studies show that a high tetragonality (c/a similar to 1.058) is maintained down to 50 angstrom thick films, suggesting indirectly that ferroelectricity is fully preserved at such small thicknesses. However, measurement of the switchable polarization (Delta P) using a pulsed probe setup and the out-of-plane piezoelectric response (d(33)) revealed a systematic drop from similar to 140 mu C/cm(2) and 60 pm/V for a 150 angstrom thick film to 11 mu C/cm(2) and 7 pm/V for a 50 angstrom thick film. This apparent contradiction between the structural measurements and the measured switchable polarization is explained by an increasing presence of a strong depolarization field, which creates a pinned 180 degrees polydomain state for the thinnest films. Existence of a polydomain state is demonstrated by piezoresponse force microscopy images of the ultrathin films. These results suggest that the limit for a ferroelectric memory device may be much larger than the fundamental limit for ferroelectricity. (c) 2006 American Institute of Physics. [less ▲]

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See detailFinite-size effects in BaTiO3 nanowires
Geneste, G.; Bousquet, Eric ULg; Junquera, J. et al

in Applied Physics Letters (2006), 88

The size dependence of the ferroelectric properties of BaTiO3 nanowires is studied from first principles. We show that the ferroelectric distortion along the wire axis disappears below a critical diameter ... [more ▼]

The size dependence of the ferroelectric properties of BaTiO3 nanowires is studied from first principles. We show that the ferroelectric distortion along the wire axis disappears below a critical diameter of about 1.2 nm. This disappearance is related to a global contraction of the unit cell resulting from low atomic coordinations at the wire surface. It is shown that a ferroelectric distortion can be recovered under appropriate tensile strain conditions. (c) 2006 American Institute of Physics. [less ▲]

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See detailDirect evidence for ferroelectric polar distortion in ultrathin lead titanate perovskite films
Despont, L.; Koitzsch, C.; Clerc, F. et al

in Physical Review. B, Condensed Matter and Materials Physics (2006), 73

X-ray photoelectron diffraction is used to directly probe the intracell polar atomic distortion and tetragonality associated with ferroelectricity in ultrathin epitaxial PbTiO3 films. Our measurements ... [more ▼]

X-ray photoelectron diffraction is used to directly probe the intracell polar atomic distortion and tetragonality associated with ferroelectricity in ultrathin epitaxial PbTiO3 films. Our measurements, combined with ab initio calculations, unambiguously demonstrate noncentrosymmetry in films a few unit cells thick, imply that films as thin as three unit cells still preserve a ferroelectric polar distortion, and also show that there is no thick paraelectric dead layer at the surface. [less ▲]

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See detailFirst-principles modeling of ferroelectric oxide nanostructures
Ghosez, Philippe ULg; Junquera, J.

in Handbook of theoretical and computational nanotechnology (2006)

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