The Experts below are selected from a list of 252 Experts worldwide ranked by ideXlab platform
Xavier Gonze - One of the best experts on this subject based on the ideXlab platform.
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Interatomic Force constants including the dft d dispersion contribution
Physical Review B, 2016Co-Authors: Benoit Van Troeye, Marc Torrent, Xavier GonzeAbstract:Grimme’s DFT-D dispersion contribution to Interatomic Forces constants, required for the computation of the phonon band structures in density-functional perturbation theory, has been derived analytically. The implementation has then been validated with respect to frozen phonons, and applied on materials where weak cohesive Forces play a major role, i.e., argon, graphite, benzene, etc. We show that these dispersive contributions have to be considered to properly reproduce the experimental vibrational properties of these materials, although the lattice parameter change, coming from the ground-state relaxation with the proper functional, induces the most important change with respect to a treatment without dispersion corrections. In the current implementation, the contribution of these dispersion corrections to the dynamical matrices (with a number of elements that is proportional to the square of the number of atoms) has only a cubic scaling with the number of atoms. In practice, the overload with respect to density-functional calculations is small, making this methodology promising to study vibrational properties of large dispersive systems.
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phonon band structure and Interatomic Force constants for bismuth crucial role of spin orbit interaction
Physical Review B, 2007Co-Authors: L E Diazsanchez, A H Romero, Xavier GonzeAbstract:The dynamical properties and the Interatomic Force constants for bismuth (Bi) are investigated from first principles with the use of density functional theory. In this context, Bi has two striking characteristics: it is a semimetal with a very small carrier density, and the spin-orbit (SO) coupling is particularly strong. To decouple these characteristics, we treat Bi as (i) nonmetallic without SO interaction, (ii) metallic with, and (iii) without SO interaction. Phonon dispersion relations and Interatomic Force constants are reported and compared with available experimental data, and very good agreement is obtained only when SO interaction is taken into account: removing this interaction causes a difference on the order of 10% in the phonon frequencies and Interatomic Force constants. Such a difference is also present in the Bi-2 molecule. We also determine which phonon bands are more affected directly by the SO interaction and which bands are indirectly affected, through changes in cell parameters. The dependence of the latter with respect to the SO coupling is also reported.
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ab initio phonon dispersion curves and Interatomic Force constants of barium titanate
Ferroelectrics, 1998Co-Authors: Philippe Ghosez, Xavier Gonze, Jeanpierre MichenaudAbstract: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.
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Interatomic Force constants in periodic solids from density functional perturbation theory
Advances in Quantum Chemistry, 1998Co-Authors: Xavier GonzeAbstract:Abstract Interatomic Force Constants (IFCs) are the proportionality coefficients between the displacements of atoms from their equilibrium positions and the Forces they induce on other atoms (or themselves). Their knowledge allows to build vibrational eigenfrequencies and eigenvectors of solids. This paper describes IFCs for different solids (SiO 2 -quartz, SiO 2 -stishovite, BaTiO 3 , Si) obtained within the Local-Density Approximation to Density-Functional Theory. An efficient variation-perturbation approach has been used to extract the linear response of wavefunctions and density to atomic displacements. In mixed ionic-covalent solids, like SiO 2 or BaTiO 3 , the careful treatment of the long-range IFCs is mandatory for a correct description of the eigenfrequencies.
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ab initio phonon dispersion curves and Interatomic Force constants of barium titanate
arXiv: Materials Science, 1997Co-Authors: Philippe Ghosez, Xavier Gonze, Jeanpierre MichenaudAbstract:The phonon dispersion curves of cubic BaTiO_3 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 KNbO_3 by Yu and Krakauer [Phys. Rev. Lett. 74, 4067 (1995)]. They reveal that correlated atomic displacements along 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 ferroelectric instability.
Andrew A. Quong - One of the best experts on this subject based on the ideXlab platform.
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first principles determination of the Interatomic Force constant tensor of au
Physical Review B, 1994Co-Authors: Andrew A. QuongAbstract:Using the plane-wave-based linear response method recently developed, the Interatomic-Force-constant tensor for the noble metal Au is obtained. Using an optimized pseudopotential to model the ion-electron interaction requires only a modest number of plane waves, and the calculated phonon dispersion curves are in excellent agreement with experiment. The Force-constant tensor is studied in detail and is compared with those obtained from Born\char21{}Von Karman fits to the experimental data. Excellent agreement with experiment is found when the range of interaction is taken to fourth neighbors, however, longer-ranged interactions need to be included to accurately determine the lattice specific heat.
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first principles determination of the Interatomic Force constant tensor of the fullerene molecule
Solid State Communications, 1993Co-Authors: Andrew A. Quong, Mark R Pederson, J L FeldmanAbstract:Abstract We have determined the full Force constant tensor (Hessian) of the fullerene molecule, C 60 from first principles. From our all-electron density functional code, the Forces on all of the atoms are calculated for different displacements of a single atom. Using finite differences and the symmetry operations of the molecule, the full matrix is determined. Diagonalization of the dynamical matrix yields the vibrational modes, which are in excellent agreement with experiment. The range and nature of the Force constant tensor will be presented.
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self consistent screening calculation of Interatomic Force constants and phonon dispersion curves from first principles
Physical Review B, 1992Co-Authors: Andrew A. Quong, B M KleinAbstract:We have developed a method for the calculation of phonon dispersion curves for crystals. The method is based upon linear response theory and makes no assumptions about the form of the ion-electron interaction or the representation of the wave functions used in the determination of the electronic structure. To demonstrate the accuracy of our method, we present a calculation of the Interatomic Force constants and the phonon dispersion curves of aluminum from first principles. In this calculation, the bare ion-electron interaction is taken as a nonlocal ab initio pseudopotential
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A Method for the Determination of Real-Space Interatomic Force-Constants.
MRS Proceedings, 1992Co-Authors: Andrew A. Quong, Barry M. KleinAbstract:ABSTRACTWe present a method for the self-consistent determination of inter-atomic Force-constants. Using non-local ab-initio pseudopotentials to represent the ion-electron interaction and linear response theory to calculate the self-consistent change in the electron density, we are able to calculate the dynamical matrices at arbitrary points in the Brillouin zone. Diagonalization of the dynamical matrix yields phonon eigenvectors and eigenvalues, and fourier inversion yields the real-space Interatomic Force-constants. We present numerical results for the phonon-dispersion of a variety of metals.
Paul Tangney - One of the best experts on this subject based on the ideXlab platform.
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a first principles based polarizable o n Interatomic Force field for bulk silica
Journal of Chemical Physics, 2010Co-Authors: James R Kermode, Paul Tangney, S Cereda, A De VitaAbstract:We present a reformulation of the Tangney–Scandolo Interatomic Force field for silica [J. Chem. Phys. 117, 8898 (2002)], which removes the requirement to perform an Ewald summation. We use a Yukawa factor to screen electrostatic interactions and a cutoff distance to limit the Interatomic potential range to around 10 A. A reparametrization of the potential is carried out, fitting to data from density functional theory calculations. These calculations were performed within the local density approximation since we find that this choice of functional leads to a better match to the experimental structural and elastic properties of quartz and amorphous silica than the generalized gradient approximation approach used to parametrize the original Tangney–Scandolo Force field. The resulting O(N) scheme makes it possible to model hundreds of thousands of atoms with modest computational resources, without compromising the Force field accuracy. The new potential is validated by calculating structural, elastic, vibrati...
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polarizable Interatomic Force field for tio2 parametrized using density functional theory
Physical Review B, 2010Co-Authors: Lars Bergqvist, Sandro Scandolo, P H Dederichs, H Muellerkrumbhaar, Jamieson K Christie, Paul TangneyAbstract:We report a classical Interatomic Force field for TiO2, which has been parametrized using density functional theory Forces, energies, and stresses in the rutile crystal structure. The reliability of this classical potential is tested by evaluating the structural properties, equation of state, phonon properties, thermal expansion, and some thermodynamic quantities such as entropy, free energy, and specific heat under constant volume. The good agreement of our results with ab initio calculations and with experimental data, indicates that our Force field describes the atomic interactions of TiO2 in the rutile structure very well. The Force field can also describe the structures of the brookite and anatase crystals with good accuracy.
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a polarizable Interatomic Force field for tio _2 parameterized using density functional theory
arXiv: Materials Science, 2009Co-Authors: Lars Bergqvist, Sandro Scandolo, P H Dederichs, Jamieson K Christie, H Mullerkrumbhaar, Paul TangneyAbstract:We report a classical Interatomic Force field for TiO$_2$, which has been parameterized using density functional theory Forces, energies, and stresses in the rutile crystal structure. The reliability of this new classical potential is tested by evaluating the structural properties, equation of state, phonon properties, thermal expansion, and some thermodynamic quantities such as entropy, free energy, and specific heat under constant volume. The good agreement of our results with {\em ab initio} calculations and with experimental data, indicates that our Force-field describes the atomic interactions of TiO$_2$ in the rutile structure very well. The Force field can also describe the structures of the brookite and anatase crystals with good accuracy.
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an ab initio parametrized Interatomic Force field for silica
Journal of Chemical Physics, 2002Co-Authors: Paul Tangney, Sandro ScandoloAbstract:We present a classical Interatomic Force field for liquid SiO2 which has been parametrized using the Forces, stresses and energies extracted from ab initio calculations. We show how inclusion of more electronic effects in a phenomenological way and parametrization at the relevant conditions of pressure and temperature allow the creation of more accurate Force fields. We compare the results of simulations with this Force field both to experiment and to the results of ab initio molecular dynamics simulations and show how our procedure leads to comparisons which are greatly improved with respect to the most widely used Force fields for silica.
Sandro Scandolo - One of the best experts on this subject based on the ideXlab platform.
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polarizable Interatomic Force field for tio2 parametrized using density functional theory
Physical Review B, 2010Co-Authors: Lars Bergqvist, Sandro Scandolo, P H Dederichs, H Muellerkrumbhaar, Jamieson K Christie, Paul TangneyAbstract:We report a classical Interatomic Force field for TiO2, which has been parametrized using density functional theory Forces, energies, and stresses in the rutile crystal structure. The reliability of this classical potential is tested by evaluating the structural properties, equation of state, phonon properties, thermal expansion, and some thermodynamic quantities such as entropy, free energy, and specific heat under constant volume. The good agreement of our results with ab initio calculations and with experimental data, indicates that our Force field describes the atomic interactions of TiO2 in the rutile structure very well. The Force field can also describe the structures of the brookite and anatase crystals with good accuracy.
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a polarizable Interatomic Force field for tio _2 parameterized using density functional theory
arXiv: Materials Science, 2009Co-Authors: Lars Bergqvist, Sandro Scandolo, P H Dederichs, Jamieson K Christie, H Mullerkrumbhaar, Paul TangneyAbstract:We report a classical Interatomic Force field for TiO$_2$, which has been parameterized using density functional theory Forces, energies, and stresses in the rutile crystal structure. The reliability of this new classical potential is tested by evaluating the structural properties, equation of state, phonon properties, thermal expansion, and some thermodynamic quantities such as entropy, free energy, and specific heat under constant volume. The good agreement of our results with {\em ab initio} calculations and with experimental data, indicates that our Force-field describes the atomic interactions of TiO$_2$ in the rutile structure very well. The Force field can also describe the structures of the brookite and anatase crystals with good accuracy.
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an ab initio parametrized Interatomic Force field for silica
Journal of Chemical Physics, 2002Co-Authors: Paul Tangney, Sandro ScandoloAbstract:We present a classical Interatomic Force field for liquid SiO2 which has been parametrized using the Forces, stresses and energies extracted from ab initio calculations. We show how inclusion of more electronic effects in a phenomenological way and parametrization at the relevant conditions of pressure and temperature allow the creation of more accurate Force fields. We compare the results of simulations with this Force field both to experiment and to the results of ab initio molecular dynamics simulations and show how our procedure leads to comparisons which are greatly improved with respect to the most widely used Force fields for silica.
J C Phillips - One of the best experts on this subject based on the ideXlab platform.
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Interatomic Force fields for silicon microclusters
Physical Review B, 1991Co-Authors: James R Chelikowsky, Keith M Glassford, J C PhillipsAbstract:We define an Interatomic potential for silicon. As with previous work, this potential is based on bulk interactions that are adjusted to describe covalent{r arrow}metallic'' phase transitions instead of small-amplitude atomic vibrations. It includes the transfer of bond strength from dangling bonds to back bonds. However, this potential has been slightly modified to reduce its range. With the modified potential we determine the energies and structural properties of Si{sub {ital n}}, where {ital n}{le}30. For {ital n}{le}10, we find this potential leads to a significant improvement over previous work for both the binding energies and the bond lengths of these clusters when compared with quantum-mechanical methods. For 10{lt}{ital n}{le}20 we find as before, and in agreement with experiment, that Si{sub {ital n}} clusters follow an icosahedral pentagonal growth sequence with {ital n}=13 and 19 being special structures. For 20{lt}{ital n}{le}30 we find this growth sequence is weakened, but a general pentagonal sequence is retained. We examine the role of back-bond strengthening by varying the strength of the corresponding interaction. We find that with increasing back-bond strength a first-order'' phase transition occurs that mimics the bulk covalent{r arrow}metallic'' transition. The ability to vary this interaction will allow us to examine intrinsicmore » differences in the nucleation of covalent versus metallic clusters.« less
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Interatomic Force fields for the structure of intrinsic point defects in silicon
Physical Review B, 1991Co-Authors: Keith M Glassford, James R Chelikowsky, J C PhillipsAbstract:On presente les calculs de l'energie et de la structure des lacunes et des defauts interstitiels intrinseques dans le silicium cristallin en utilisant un champ de Forces interatomiques developpe recemment. Le potentiel classique utilise inclut explicitement les effets quantiques. Les resultats sont compares a ceux des calculs ab initio de la mecanique quantique dans l'approximation de la densite locale (LDA), de l'approche empirique de la liaison forte (TB), et des autres potentiels classiques. La structure de ces defauts telle que determinee par le present potentiel est un bon accord avec celle obtenue a partir des calculs purement de la mecanique quantique. Les presentes estimations des energies de formation de ces defauts excedent de quelque peu les valeurs obtenues a partir des calculs de la mecanique quantique. On attribue ces differences aux distortions Jahn-Teller qui ne sont pas incluses dans les potentiels classiques, et a une petite surestimation de la «raideur» du reseau cristallin
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surface and thermodynamic Interatomic Force fields for silicon clusters and bulk phases
Physical Review B, 1990Co-Authors: James R Chelikowsky, J C PhillipsAbstract:We have developed new Interatomic Force fields which describe the phase stability of crystalline silicon and small clusters of silicon. We show that when three-body Forces are adjusted to describe covalent{r arrow}metallic'' phase transitions instead of small-amplitude atomic vibrations, a simple and accurate Force field is obtained. This Force field can be easily modified to describe energies and structures of Si{sub {ital n}} vapor-phase clusters. A key aspect of the cluster problem is the transfer of bond strength from dangling bonds to back bonds. We expect our potential will have widespread applications to the formation and activation energies for diffusion of defects in crystalline Si and to the structural properties of amorphous and liquid silicon.