References of "Raty, Jean-Yves"
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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 detailAdsorption of selenium wires in silicalite-1 zeolite: a first order transition in a microporous system
Bichara, C.; Raty, Jean-Yves ULg; Pellenq, RJ-M

in Physical Review Letters (2002), 89(1), 016101-1-016101-016101-4016101-016101-4

A tight binding grand canonical Monte Carlo simulation of the adsorption of selenium in silicalite-1 zeolite is presented. The calculated adsorption-desorption isotherms exhibit characteristic features of ... [more ▼]

A tight binding grand canonical Monte Carlo simulation of the adsorption of selenium in silicalite-1 zeolite is presented. The calculated adsorption-desorption isotherms exhibit characteristic features of a first order transition, unexpected for adsorption in a microporous system with pore size of the order of 0.5 to 0.6 nm. We analyze this behavior as a result of the favored twofold coordinated chain structure of selenium that grows inside the complex three-dimensional microchannel network of silicalite. This analysis is confirmed by simpler calculations of a lattice gas-type model [less ▲]

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See detailComputer simulation of liquid semiconductors
Bichara, C.; Gaspard, Jean-Pierre ULg; Raty, Jean-Yves ULg

in Journal of Non-Crystalline Solids (2002), 312

We discuss two examples of computer simulation of liquid semiconductors by two different techniques. Both examples are concerned with the relationship between thermodynamic properties and the atomic ... [more ▼]

We discuss two examples of computer simulation of liquid semiconductors by two different techniques. Both examples are concerned with the relationship between thermodynamic properties and the atomic structure in the liquid state. By means of ab initio molecular dynamics we analyze the atomic structure of liquid Ge15Te85 eutectic alloys. We show that the changes observed in the experimental total structure factor S(q) are located in the GeTe partial structure factor, the TeTe partial structure factor remaining essentially unaltered. Using a semi-empirical tight binding approach, coupled with Gibbs ensemble and constant pressure Monte Carlo calculations, we can calculate the liquid vapor equilibrium of selenium. We obtain a liquid-vapor equilibrium curve and a critical point in the correct range of magnitude and an atomic structure of the liquid phase in good agreement with the experimental data. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailDistance correlations and dynamics of liquid GeSe: An ab initio molecular dynamics study
Raty, Jean-Yves ULg; Godlevsky, V. V.; Gaspard, Jean-Pierre ULg et al

in Physical Review. B, Condensed Matter and Materials Physics (2001), 64

We analyze the structure and dynamics of semiconducting liquid GeSe using ab initio molecular-dynamics simulations. We show the local order of the liquid to be close to that of the low-temperature ... [more ▼]

We analyze the structure and dynamics of semiconducting liquid GeSe using ab initio molecular-dynamics simulations. We show the local order of the liquid to be close to that of the low-temperature crystalline phase. alpha -GeSe. In particular, we show that the Peierls distortion, which defines the a phase and vanishes in the high-temperature beta crystalline phase, reenters GeSe in the melt. Examining the distance histograms allows one to analyze the Ge environment as consisting of a Gese(3) unit and having one Ge-Ge defective bond. Evidence is presented that Peierls distortion is directly responsible for the semiconducting behavior of the melt. The calculated viscosity and electrical conductivity are in agreement with the experiment. An additional neutron-diffraction experiment indicates that this liquid structure is unmodified 200 K above the melting point. [less ▲]

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See detailAb initio simulations of liquid semiconductors using the pseudopotential-density functional method
Chelikowsky, J. R.; Derby, J. J.; Godlevsky, V. V. et al

in Journal of Physics : Condensed Matter (2001), 13(41), 817-854854

One of the most difficult problems in condensed matter physics is describing the microscopic nature of the liquid state. Owing to the dynamical nature of the liquid state, it is not possible to discuss a ... [more ▼]

One of the most difficult problems in condensed matter physics is describing the microscopic nature of the liquid state. Owing to the dynamical nature of the liquid state, it is not possible to discuss a particular microscopic structure; only ensemble averages can be specified. Such averages can be performed via well crafted molecular dynamics simulations: the length of the simulation, the size of the ensemble and the nature of the interatomic forces must all be carefully analysed. Historically, a problematic issue in doing such simulations is that of how to describe the interatomic forces in the liquid state. This matter is especially challenging for the melt of semiconductors, such as silicon or gallium arsenide, where the chemical bond contains a strong covalent component. It is difficult to use pairwise interatomic potentials in such cases. Although many-body potentials can be utilized for simulations of these materials, one must map quantum phenomena such as hybridization onto classical interatomic potentials. This mapping is complex and difficult. In this review, we illustrate how one can avoid this problem by utilizing quantum forces to simulate liquids. Our focus is on the pseudopotential-density functional method. Within the pseudopotential method, only the valence electrons are explicitly treated and within the density functional theory, exchange and correlation terms are mapped onto an effective one-electron potential [less ▲]

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See detailEvidence of a reentrant Peierls distortion in liquid GeTe
Raty, Jean-Yves ULg; Godlevsky, V.; Ghosez, Philippe ULg et al

in Physical Review Letters (2000), 85(9), 1950-1953

The local atomic order of semiconducting liquid GeTe is studied using first-principles molecular-dynamics simulations. Our work points out a high degree of alternating chemical order in the liquid and ... [more ▼]

The local atomic order of semiconducting liquid GeTe is studied using first-principles molecular-dynamics simulations. Our work points out a high degree of alternating chemical order in the liquid and demonstrates the presence of a Peierls distortion close above the melting temperature. This distortion, absent in the high temperature crystalline structure of NaCl type, is a remnant of the atomic arrangement in the A7 low temperature crystalline phase. It disappears slowly with temperature, as the liquid evolves from a semiconducting to a metallic state. [less ▲]

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See detailStructural and electronic properties of high-temperature fluid selenium
Raty, Jean-Yves ULg; Saul, A.; Gaspard, Jean-Pierre ULg et al

in Computational Materials Science (2000), 17(2-4), 239-242242

A semi-empirical tight-binding energy model is developed for selenium. It includes s and p electrons as well as an empirical description of the dispersion forces. The band structure parameters are ... [more ▼]

A semi-empirical tight-binding energy model is developed for selenium. It includes s and p electrons as well as an empirical description of the dispersion forces. The band structure parameters are obtained by fitting ab initio calculations. The simulated liquid structures are in very good agreement with the most recent X-ray scattering and EXAFS measurements. The Monte Carlo simulations performed show that the complex liquid structures observed result from the breaking and branching of the selenium chains. The total coordination number is shown to result from the balance between one-, two- and three-fold coordinated atoms. The role of these defects is discussed in relationship with the electrical conductivity of the liquid, i.e. the semiconductor-metal and metal-non-metal transitions observed at high pressure and temperature [less ▲]

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See detailRe-entrant Peierls distortion in IV-VI compounds
Raty, Jean-Yves ULg; Gaspard, Jean-Pierre ULg; Bichara, C. et al

in Physica B: Condensed Matter (2000), 276-278

At room temperature, the local structure of crystalline group V elements (As, Sb,middotmiddotmiddot) and their IV-VI isoelectronic compounds (GeSe,middotmiddotmiddot) is governed by a Peierls distortion ... [more ▼]

At room temperature, the local structure of crystalline group V elements (As, Sb,middotmiddotmiddot) and their IV-VI isoelectronic compounds (GeSe,middotmiddotmiddot) is governed by a Peierls distortion of the simple cubic or NaCl structure which is a symmetry breaking electronic instability. The morphology of the distortion is determined by the filling ratio of the p-band; for a half-filled p-band, the sixfold coordination becomes 3 (short, covalent) +3 (long, van der Waals). In general, at high temperature, the structure recovers its higher coordination number. Neutron diffraction experiments have been made in the liquid state at lambda=0.7 Aring. It is observed that the Peierls distortion is still present in the liquid for most IV-VI compounds. This behavior is observed and discussed for a series of Sn and Ge chalcogenides: SnS, SnSe, GeS, GeSe and GeTe and their temperature evolution is discussed. GeSe and GeTe show an interesting re-entrant phase behavior. The heaviest IV-VI compound SnTe does not show a distorted state. We demonstrate that the hardness of the repulsive potential is a key parameter in this mechanism [less ▲]

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See detailLocal order of the high-pressure metallic phase of liquid selenium: a diffraction study
Raty, Jean-Yves ULg; Gaspard, Jean-Pierre ULg; Le Bihan, T. et al

in Journal of Physics : Condensed Matter (1999), 11(50), 10243-1024910249

Liquid selenium undergoes a phase transition towards a metallic phase when sufficient pressure is applied. We performed an x-ray diffraction experiment at the 1D30 beamline of the ESRF at the wavelength ... [more ▼]

Liquid selenium undergoes a phase transition towards a metallic phase when sufficient pressure is applied. We performed an x-ray diffraction experiment at the 1D30 beamline of the ESRF at the wavelength of 0.149 Aring to investigate the local order of the metallic liquid. The diffraction pattern of liquid Se has been recorded with the large-volume Paris-Edinburgh cell between (20degC, 3 GPa) and (1650degC, 4.1 GPa). The local order of the metallic liquid selenium is found to be close to that of liquid tellurium. In particular, the coordination number Z increases with temperature from 2.6 to 3.0 [less ▲]

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See detailOn the structure of liquid IV-VI semiconductors
Raty, Jean-Yves ULg; Gaspard, Jean-Pierre ULg; Bionducci, M. et al

in Journal of Non-Crystalline Solids (1999), 250-252

The crystalline structure of most stoichiometric IV-VI semiconductors can be viewed as a distortion of the NaCl structure; the distortion amplitude depends on the components. As a result, corrugated ... [more ▼]

The crystalline structure of most stoichiometric IV-VI semiconductors can be viewed as a distortion of the NaCl structure; the distortion amplitude depends on the components. As a result, corrugated planes of covalently bonded atoms are linked by dispersion (Van der Waals) forces. Neutron scattering experiments were performed on the liquid phases of a series of IV-VI compounds (GeS, GeSe, GeTe, SnS, SnSe and SnTe). We show that the evolution of the local order is correlated with the conductivity measurements [less ▲]

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See detailStructure of high temperature fluid selenium
Bichara, C.; Raty, Jean-Yves ULg; Gaspard, Jean-Pierre ULg

in Journal of Non-Crystalline Solids (1999), 250-252

Monte Carlo simulations based on a semi empirical tight binding model including dispersion forces were performed to study liquid selenium at temperatures between 600 and 2000 K. The atomic structures ... [more ▼]

Monte Carlo simulations based on a semi empirical tight binding model including dispersion forces were performed to study liquid selenium at temperatures between 600 and 2000 K. The atomic structures obtained are in agreement with the X-ray scattering and extended X-ray absorption fine structure (EXAFS) data in a range of temperatures and densities. A correlation between the conductivity of high temperature fluid selenium and the degree of branching and breaking of the selenium chains is observed [less ▲]

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See detailStructure of high-temperature fluid selenium
Raty, Jean-Yves ULg; Saul, A.; Gaspard, Jean-Pierre ULg et al

in Physical Review. B : Condensed Matter (1999), 60(4), 2441-24482448

A semiempirical tight-binding energy model is developed for selenium. It includes s and p electrons as well as an empirical description of the dispersion forces that proves necessary at the liquid ... [more ▼]

A semiempirical tight-binding energy model is developed for selenium. It includes s and p electrons as well as an empirical description of the dispersion forces that proves necessary at the liquid densities under study. The band-structure parameters are obtained by fitting abinitio calculations. The simulated liquid structures are in very good agreement with the most recent X-ray scattering and extended X-ray absorption fine-structure experiments in a broad temperature and density range. The Monte Carlo simulations performed show that the complex liquid structures observed result from the breaking and branching of the selenium chains. The total coordination number is shown to result from the balance between one-, two-, and threefold coordinated atoms. The role of these defects is discussed in relationship with the electrical conductivity of the liquid, i.e., the semiconductor-metal and metal-nonmetal transitions observed at high pressures [less ▲]

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See detailEvolution of the Peierls distortion in liquid AsxSb1-x compounds
Raty, Jean-Yves ULg; Gaspard, Jean-Pierre ULg; Céolin, R. et al

in Journal of Non-Crystalline Solids (1998), 232-234

The local order in the liquid binary alloy AsxSb1-x (0 ≤ x ≤ 1) is studied by short-wavelength (λ = 0.7 Å) neutron scattering. The coordination number (Z) and the interatomic distances (d) are analyzed in ... [more ▼]

The local order in the liquid binary alloy AsxSb1-x (0 ≤ x ≤ 1) is studied by short-wavelength (λ = 0.7 Å) neutron scattering. The coordination number (Z) and the interatomic distances (d) are analyzed in terms of the As concentration: Z increases continuously, from a value of 3.5 for pure arsenic to a value of 6.3 for pure antimony, whereas d shows a departure from Vegard's rule. The interatomic distance increases in the range 0.15 ≤ x ≤ 1.00 and is almost constant in the range 0.00 ≤ x ≤ 0.15. A simple tight-binding model is developed, which indicates that the relevant parameter is the hardness of the core repulsion between the atoms. © 1998 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailEvolution of the Peierls distortion in liquid As xSb 1-x compounds
Raty, Jean-Yves ULg; Gaspard, Jean-Pierre ULg; Ceolin, R. et al

in Journal of Non-Crystalline Solids (1998), 232-234

The local order in the liquid binary alloy As xSb 1-x (0lesxles1) is studied by short-wavelength (lambda=0.7 Aring) neutron scattering. The coordination number (Z) and the interatomic distances (d) are ... [more ▼]

The local order in the liquid binary alloy As xSb 1-x (0lesxles1) is studied by short-wavelength (lambda=0.7 Aring) neutron scattering. The coordination number (Z) and the interatomic distances (d) are analyzed in terms of the As concentration: Z increases continuously, from a value of 3.5 for pure arsenic to a value of 6.3 for pure antimony, whereas d shows a departure from Vegard's rule. The interatomic distance increases in the range 0.15lesxles1.00 and is almost constant in the range 0.00lesxles0.15. A simple tight-binding model is developed, which indicates that the relevant parameter is the hardness of the core repulsion between the atoms [less ▲]

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See detailCovalent liquids: tight binding simulation versus experimental results
Gaspard, Jean-Pierre ULg; Bichara, C.; Raty, Jean-Yves ULg et al

(1998)

We show that a simple tight binding model with a repulsive potential describes the Peierls distortions in covalent systems and the well-known octet rule. The existence and the intensity of the Peierls ... [more ▼]

We show that a simple tight binding model with a repulsive potential describes the Peierls distortions in covalent systems and the well-known octet rule. The existence and the intensity of the Peierls distortion is mainly related to the hardness of the repulsive potential as demonstrated both by theoretical calculations and by the experimental systematic analysis of liquid structures. In particular, As is threefold coordinated and Sb is sixfold coordinated in the liquid; the qualitative difference is explained by the ratio of the distortion energy DeltaE to the thermal energy k BT. The As xSb 1-x alloys show continuously varying average coordination numbers showing that the semiconductor-metal transition is continuous with concentration. In addition, we illustrate in the case of liquid Se that, tight binding Monte Carlo simulations are able to describe quantitatively the structure of liquid elements provided the Van der Waals potential is added [less ▲]

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See detailA cinnabar local order in liquid II-VI compounds
Raty, Jean-Yves ULg; Gaspard, Jean-Pierre ULg; Ceolin, R. et al

in Physica B: Condensed Matter (1997)

A short wavelength (lambda=0.7 Aring) neutron scattering experiment has been performed on the II-VI compounds HgS, HgSe and Zn xHg 1-xTe. Liquid HgS can be viewed as a distortion of the blende structure ... [more ▼]

A short wavelength (lambda=0.7 Aring) neutron scattering experiment has been performed on the II-VI compounds HgS, HgSe and Zn xHg 1-xTe. Liquid HgS can be viewed as a distortion of the blende structure; we show that this distortion decreases gradually with temperature. For Zn xHg 1-xTe, we show that the transition between the six coordinated HgTe liquid and the four coordinated ZnTe liquid is not continuous, the intermediate phase being a deformed cinnabar one [less ▲]

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See detailOn the structure of liquid tellurium
Bichara, C.; Raty, Jean-Yves ULg; Gaspard, Jean-Pierre ULg

in Journal of Non-Crystalline Solids (1996), 205-207

The atomic structure and the bonding mechanism in liquid tellurium are investigated by a tight binding Monte Carlo technique. The chain structure is preserved but a third covalent bond emerges with an ... [more ▼]

The atomic structure and the bonding mechanism in liquid tellurium are investigated by a tight binding Monte Carlo technique. The chain structure is preserved but a third covalent bond emerges with an intermediate interatomic separation (3.15 Aring). In addition a bond length alternation inside the chain appears in agreement with recent EXAFS experiments and the valence angles are significantly reduced. The electronic structure is studied and particular attention is paid to the modifications of lone pair interactions in the liquid structure [less ▲]

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See detailLocal orders in II-VI liquid compounds
Gaspard, Jean-Pierre ULg; Raty, Jean-Yves ULg; Ceolin, R. et al

in Journal of Non-Crystalline Solids (1996), 205-207

The structure of liquid CdTe, HgTe and ZnTe is studied by neutron scattering. Upon melting, drastically different behaviors are found: CdTe and ZnTe keep their fourfold coordination in the melt and remain ... [more ▼]

The structure of liquid CdTe, HgTe and ZnTe is studied by neutron scattering. Upon melting, drastically different behaviors are found: CdTe and ZnTe keep their fourfold coordination in the melt and remain semiconductors, whereas HgTe becomes sixfold coordinated and metallic. This dissimilarity is discussed in terms of the electronegativity difference and of the repulsive potential hardness. Entropic aspects are also discussed [less ▲]

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See detailStructure and bonding in liquid tellurium
Bichara, C.; Raty, Jean-Yves ULg; Gaspard, Jean-Pierre ULg

in Physical Review. B, Condensed Matter and Materials Physics (1996), 53(1), 206-211211

The atomic structure and bonding mechanism in liquid tellurium have been investigated by a tight-binding Monte Carlo simulation. On melting, the chain structure of the crystal is preserved in spite of ... [more ▼]

The atomic structure and bonding mechanism in liquid tellurium have been investigated by a tight-binding Monte Carlo simulation. On melting, the chain structure of the crystal is preserved in spite of some significant changes in the local atomic environment. A third covalent bond appears with a bond length (widely distributed around 3.15 Aring) intermediate between those characteristic of the crystal. A short-long alternation of the bonds takes place within the chains, in agreement with the most recent extended X-ray-absorption fine structure measurements. In addition, the bond angle within the chains is reduced. Our calculations clearly prove that these effects are due to the electronic interaction between the lone pair orbitals. The subsequent broadening of the lone pair band is responsible for the semiconductor to metal transition that takes place upon melting. [less ▲]

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See detail2D cellular automata for turbulent convection
Perdang, Jean ULg; Raty, Jean-Yves ULg; Tomassini, M. et al

in Gruber, R.; Tomassini, M. (Eds.) Proceedings of the 6th Joint EPS-APS International Conference on Physics Computing. PC'94. Physics Computing '94 (1994)

A cellular automaton (CA) formulation is devised to simulate 2-dimensional Rayleigh-Benard convection. The model is tested in the case of a standard plane-parallel shallow configuration for which ... [more ▼]

A cellular automaton (CA) formulation is devised to simulate 2-dimensional Rayleigh-Benard convection. The model is tested in the case of a standard plane-parallel shallow configuration for which analytical solutions of the hydrodynamical formulation are available at low enough Rayleigh numbers. If we use a measure of the intensity of gravity, k, as our free parameter (the analogue of the Rayleigh number), all other model parameters being fixed, then we can reproduce the well-known stationary roll-pattern predicted by the hydrodynamic theory at low k values. At higher k values the model exhibits a nonstationary turbulent flow pattern. Our formulation is extended to less trivial geometries for which an analytic treatment in the usual hydrodynamic context is not feasible. Besides geometry-constrained stationary patterns of motion in a range of low k values, this model exhibits again turbulent motions at higher k values [less ▲]

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