Showing papers on "Interatomic potential published in 1998"
TL;DR: In this paper, the results of room-and low-temperature measurements of second-order Raman scattering for perfect GaN and AlN crystals as well as the Raman-scattering data for strongly disordered samples are presented.
Abstract: We present the results of room- and low-temperature measurements of second-order Raman scattering for perfect GaN and AlN crystals as well as the Raman-scattering data for strongly disordered samples. A complete group-theory analysis of phonon symmetry throughout the Brillouin zone and symmetry behavior of phonon branches, including the analysis of critical points, has been performed. The combined treatment of these results and the lattice dynamical calculations based on the phenomenological interatomic potential model allowed us to obtain the reliable data on the phonon dispersion curves and phonon density-of-states functions in bulk GaN and AlN. @S0163-1829~98!06840-4#
725 citations
TL;DR: In this paper, the authors developed an empirical potential for silicon which represents a considerable improvement over existing models in describing local bonding for bulk defects and disordered phases, and applied it to the relaxation of point defects, core properties of partial dislocations and the structure of disordered phase, none of which are included in the fitting procedure.
Abstract: We develop an empirical potential for silicon which represents a considerable improvement over existing models in describing local bonding for bulk defects and disordered phases. The model consists of two- and three-body interactions with theoretically motivated functional forms that capture chemical and physical trends as explained in a companion paper. The numerical parameters in the functional form are obtained by fitting to a set of ab initio results from quantum-mechanical calculations based on density-functional theory in the local-density approximation, which include various bulk phases and defect structures. We test the potential by applying it to the relaxation of point defects, core properties of partial dislocations and the structure of disordered phases, none of which are included in the fitting procedure. For dislocations, our model makes predictions in excellent agreement with ab initio and tight-binding calculations. It is the only potential known to describe both the 30°- and 90°-partial dislocations in the glide set$111%. The structural and thermodynamic properties of the liquid and amorphous phases are also in good agreement with experimental and ab initio results. Our potential is capable of simulating a quench directly from the liquid to the amorphous phase, and the resulting amorphous structure is more realistic than with existing empirical preparation methods. These advances in transferability come with no extra computational cost, since force evaluation with our model is faster than with the popular potential of Stillinger-Weber, thus allowing reliable atomistic simulations of very large atomic systems. @S0163-1829~98!04026-0#
406 citations
TL;DR: In this paper, a physical mechanism for tuning the atom-atom interaction strength at ultralow temperatures was proposed, in which in the presence of a dc electric field the interatomic potential is changed due to the effective dipole-dipole interaction between the polarized atoms.
Abstract: We propose a physical mechanism for tuning the atom-atom interaction strength at ultralow temperatures. In the presence of a dc electric field the interatomic potential is changed due to the effective dipole-dipole interaction between the polarized atoms. Detailed multichannel scattering calculations reveal features never before discussed for ultracold atomic collisions. We demonstrate that optimal control of the effective atom-atom interactions can be achieved under reasonable laboratory conditions. Implications of this research on the physics of atomic Bose-Einstein condensation and on the pursuit for atomic degenerate fermion gases will be discussed.
128 citations
TL;DR: In this paper, a new empirical interatomic potential of the embedded atom type is developed for the Fe-Cu system, which is used in simulation studies of the interface of small coherent Cu precipitates in and of dislocation core structure.
Abstract: A new empirical interatomic potential of the embedded atom type is developed for the Fe-Cu system. The potential for the alloy system was constructed to reproduce known physical parameters of the alloy, such as the heat of solution of Cu in Fe and the binding energy of a vacancy and a Cu atom in the matrix. The potential also reproduces first-principle calculations of the properties of metastable phases in the system. This atomic interaction model was used in simulation studies of the interface of small coherent Cu precipitates in and of dislocation core structure. The phase stability of the body-centred cubic Cu precipitates was also analysed.
100 citations
TL;DR: In this paper, the damage produced in α-zirconium at 100 K by displacement cascades with energy, E p, up to 20 keV has been investigated by molecular dynamics using a many-body interatomic potential.
83 citations
TL;DR: In this article, the results of molecular dynamics simulations of gadolinium zirconate (Gd 2 Zr 2 O 7 ), an oxide fast ion conductor with the pyrochlore structure, are presented.
83 citations
TL;DR: In this article, the authors describe the distributions of reflected ion energies, Er, reflected ion angles (polar, θr; azimuthal, φr; and total scatter, αr), obtained via MD simulations of Ar+ bombardment of model SiO2 surfaces.
Abstract: Numerous profile evolution simulation studies strongly suggest that ions reflecting with glancing angles from etched feature sidewalls are responsible for microtrench formation at the feature bottom. Within these studies such reflections are traditionally assumed specular, where the ion retains all of its incident energy. In this study, we gauge the validity of that assumption by describing the distributions of reflected ion energies, Er, reflected ion angles (polar, θr; azimuthal, φr; and total scatter, αr), obtained via MD simulations of Ar+ bombardment of model SiO2 surfaces. We modeled the physics of the surface atom interactions using an empirical interatomic potential energy function developed by Feuston and Garofalini [J. Chem Phys. 89, 5818 (1988)]. We considered Ar+ ion energies, Ei, of 100 and 200 eV, and incident polar angles, θi, of 0°, 30°, 45°, 60°, 75°, and 85°, measured from the macroscopic surface normal. Each (Ei,θi) combination was used to generate a unique roughened model oxide surface...
78 citations
TL;DR: In this paper, a Finnis/Sinclair-type interatomic potential for copper is used to examine the properties of dissociated screw dislocations in the face-centred cubic lattice.
Abstract: A Finnis/Sinclair-type interatomic potential for copper is used to examine the properties of dissociated screw dislocations in the face-centred cubic lattice The critical stress for dislocation motion is found to be a sensitive function of the partial dislocation separation, with a lower limit at least 85% smaller than the Peierls stress The constriction of Heidenreich-Shockley partials is modelled using an applied stress which interacts only with the edge Burgers vectors; recombination is not observed, but there is a critical separation below which the potential energy of the dislocation rises very rapidly The classical model of cross-slip, in which the dislocation cannot leave its slip plane unless it is fully constricted, is found to be incorrect Instead, cross-slip is possible at all partial separations, provided the driving stress is large enough Finally, a new mechanism for cross-slip nucleation is described
75 citations
TL;DR: In this paper, the Hartree-Fock (HF) method is combined with ab initio-parametrized ion pair shell model potential functions, and the combined QM-Pot relative stabilities and reaction energies deviate from the periodic full QM results by 4-9 kJ/mol only, which demonstrates the power of the combined approach.
Abstract: Comparison is made between a combined quantum mechanics/interatomic potential function approach (QM-Pot) and its fully quantum-mechanical limit, ab initio calculation applying periodic boundary conditions. The Hartree–Fock (HF) method is combined with ab initio-parametrized ion pair shell model potential functions. The CRYSTAL code is employed for the periodic Hartree–Fock calculations. The same double-/valence triple-zeta polarization basis sets are used in both the approaches. The proton siting and ammonia adsorption in a high-silica acidic zeolite catalyst, H-chabazite (Si/Al=11, space group P1, unit cell H–AlO2[SiO2]11) are examined. The combined QM-Pot relative stabilities and reaction energies deviate from the periodic full QM results by 4–9 kJ/mol only, which demonstrates the power of our combined approach. This conclusion is also supported by comparison of the electrostatic potential inside the zeolite pore, calculated from the periodic wave function and by the QM-Pot approach. Framework oxygen O1...
66 citations
TL;DR: The radial distribution function for liquid aluminum oxide (corundum) is calculated by means of the two-phase molecular-dynamics method utilizing a previously developed pairwise interatomic potential as mentioned in this paper.
Abstract: The radial distribution function G(r) for liquid aluminum oxide (corundum) is calculated by means of the two-phase molecular-dynamics method utilizing a previously developed pairwise interatomic potential. Our results agree very well with the recent exper
45 citations
TL;DR: In this article, a combined quantum mechanics-intermolecular potential function approach (QM-Pot) is used at the DFT level to predict the structures and properties of Bronsted acid sites in an aluminosilicate and a silico-aluminophosphates (SAPO) with the chabazite framework structure.
Abstract: DFT-B3LYP calculations are performed on 4-ring models of aluminophosphates (AlPOs) and silico-aluminophosphates (SAPOs). The results are used to fit the parameters of ion pair shell model potential functions. The potentials obtained are tested in lattice energy minimizations for berlinite and the microporous materials AlPO-18, AlPO-40, AlPO-52, and VPI-5. Not only does the potential reproduce the observed structures (average error of the cell constants 1.3%), it also predicts vibrational frequencies over the whole frequency range equally well (maximum deviation 50 cm -1 ). The potential is used to predict the structures and properties of Bronsted acid sites in an aluminosilicate and a SAPO with the chabazite framework structure (HSSZ-13 and HSAPO-34). A new combined quantum mechanics-intermolecular potential function approach (QM-Pot) is used at the DFT level. Comparison is made with full periodic DFT calculations using plane wave basis sets. The deprotonation energies corrected for systematic errors of the methods used are 1 231-1 235 and 1 261-1 280 kJ/mol for HSSZ-13 and HSAPO-34, respectively. The same acid site has a lower acidity in a SAPO than in an aluminosilicate zeolite of the same structure.
TL;DR: In this article, a two-body interatomic potential model for GeO2 polymorphs has been determined to simulate the structure change of them by semi-empirical procedure, total lattice energy minimization of GeO 2 polymorphs.
Abstract: A two-body interatomic potential model for GeO2 polymorphs has been determined to simulate the structure change of them by semi-empirical procedure, total lattice energy minimization of GeO2 polymorphs. Based on this potential, two polymorphs of GeO2; α-quartz-type and rutile-type, have been reproduced using the molecular dynamics (MD) simulation techniques. Crystal structures, bulk moduli, volume thermal expansion coefficients and enthalpies of these polymorphs of GeO2 were simulated. In spite of the simple form of the potential, these simulated structural values, bulk moduli and thermal expansivities are in excellent agreement with the reliable experimental data in respect to both polymorphs. Using this potential, MD simulation was further used to study the structural changes of GeO2 under high pressure. We have investigated the pressure-induced amorphization. As reported in previous experimental studies, quartz-type GeO2 undergoes pressure-induced crystalline-to-amorphous transformation at room temperature, the same as other quartz compounds; SiO2, AlPO4. Under hydrostatic compression, in this study, α-quartz-type GeO2 transformed to a denser amorphous state at 7.4 GPa with change of the packing of oxygen ions and increase of germanium coordination. At higher pressure still, rutile-type GeO2 transformed to a new phase of CaCl2-type structure as a post-rutile candidate.
27 Jan 1998
TL;DR: In this article, the melting curve of corundum is calculated by using two approaches: the first one is conventional and the second one is two-phase molecular dynamics method both utilizing the same pairwise interatomic potential developed earlier on.
Abstract: The melting curve of corundum is calculated by using two approaches: the first one is conventional and the second one is two-phase molecular dynamics method both utilizing the same pairwise interatomic potential developed earlier on. The melting curve obtained by the two-phase simulation method is in agreement with the existing experimental data up to 25 GPa. A comparison of melting curves obtained by a two-phase simulation method and a conventional molecular dynamic method in NPT ensemble demonstrates a substantial overestimation of melting temperatures when applying conventional molecular dynamic technique. The inaccuracy of the conventional method increases with increasing pressure and, in the case of corundum, changes from about 300 K at 1 bar to about 1000 K at 1 Mbar.
TL;DR: In this paper, the volume dependence of the total energy of these materials computed by first-principles augmented-plane-wave calculations has been derived and applied to calculate the bulk modulus and elastic constants of pure elements and alloys.
Abstract: We have evaluated interatomic potentials of Cu, Au and Cu-Au ordered alloys in the framework of the second-moment approximation to the tight-binding theory by fitting to the volume dependence of the total energy of these materials computed by first-principles augmented-plane-wave calculations. We have applied this scheme to calculate the bulk modulus and elastic constants of the pure elements and alloys and we have obtained a good agreement with experiment. We also have performed molecular-dynamics simulations at various temperatures, deducing the temperature dependence of the lattice constants and the atomic mean square displacements, as well as the phonon density of states and the phonon-dispersion curves of the ordered alloys. A satisfactory accuracy was obtained, comparable to previous works based on the same approximation, but resulting from fitting to various experimental quantities.
TL;DR: In this article, anisotropic measurements of the momentum distribution and the mean Laplacian of the interatomic potential ∇2V have been performed using electron volt neutrons, with wave vector transfers between 24 A−1 and 98 A− 1.
Abstract: Neutron Compton scattering (NCS) measurements of the anisotropy of the momentum distribution and the mean Laplacian of the interatomic potential ∇2V have been performed using electron volt neutrons, with wave vector transfers between 24 A−1 and 98 A−1. The measured momentum distribution of the atoms displays significantly more anisotropy than a calculation using a model density of states. We have observed anisotropies in ∇2V for the first time. The results suggest that the atomic potential is harmonic within the graphite planes, but anharmonic for vibrations perpendicular to the planes.
TL;DR: In this article, a structural unit model was developed for the structure of the high-index surfaces on the basis of a few low-energy surfaces, and the model can predict the structural features and also give an estimate of the energies of the higher index surfaces.
TL;DR: In this article, the Gibbs free energy values derived from molecular dynamics simulations using a non-empirical interatomic potential were used to accurately predict diffusion in MgO at zero pressure.
Abstract: Theoretical calculations of diffusion in periclase were performed to model the rheological properties of the lower mantle. Gibbs free energy values derived from molecular dynamics simulations using a non-empirical interatomic potential to accurately predict diffusion in MgO at zero pressure. Diffusion coefficients were computed for pressures and temperatures up to 140 GPa and 5000 K. We find that Mg vacancies required for diffusive transport are likely extrinsic (due to impurities), and the resulting O vacancies would then be too few to support bulk O transport. Estimates of viscosity from these results are consistent with those inferred for the lower mantle from geophysical observations if grain boundary diffusion is responsible for O transport.
TL;DR: In this article, the acceptor center identified by Hall-effect measurements and EPR is found to be related to the delocalized hole shared by the four As neighbours bound to CdGe.
Abstract: Native acceptor centres in are studied using atomistic simulation techniques for which a new set of interatomic potential parameters consisting of two- and three-body terms is developed. Crystal lattice constants, elastic and low- and high-frequency dielectric constants are well reproduced in this atomistic model. The calculated formation energies for vacancies, interstitials and antisites in this material suggest that the intrinsic disorder is dominated by antisites in the cation sublattice followed by the Schottky and Frenkel defects. The acceptor centre identified by Hall-effect measurements and EPR is found to be related to the delocalized hole shared by the four As neighbours bound to CdGe. For this centre, calculations yield a binding energy of 0.13 eV in an agreement with the experimental value of 0.15 eV obtained by the Hall-effect measurements. Furthermore calculations provide the magnitude of the lattice distortion introduced by this acceptor centre in which can be used for the analysis of ENDOR experiments.
TL;DR: In this paper, the defect structure of tin-doped α-Fe2O3 has been assessed using interatomic potential calculations, and it was shown that a structure involving tin (or titanium) partially substituting at the octahedral iron sites as well as partially occupying the empty interstitial octagonal sites in corundum-related α-FE3 is more favorable than an alternative model in which the tin ions only occupy the empty intact interstitial sites.
TL;DR: In this paper, the authors apply the Moleculardynamics (MD) and the Embedded Atom Method (EAM) to calculate the viscosity of a liquid transition metal, namely Ni.
TL;DR: In this article, the defect-formation process in silicon grown from the melt based on the ordinary Langevin equation employing the Tersoff interatomic potential was examined and it was shown that hexagonal structures are formed near the solid-liquid interfaces and these regions give rise to microfacets composed of primarily {111} planes.
Abstract: We have performed molecular-dynamics calculations to examine defect-formation processes in silicon grown from the melt based on the ordinary Langevin equation employing the Tersoff interatomic potential. Our simulations indicated that hexagonal structures are formed near the solid-liquid interfaces and these regions give rise to microfacets composed of primarily {111} planes. Most of these hexagonal configurations were annihilated during further crystal growth, but a part of them were left, which resulted in defect formation with five- and seven-member rings.
TL;DR: In this article, the free energies of unstable stacking fault (USF) configurations on the glide and shuffle slip planes in silicon were calculated using the recently developed Environment Dependent Interatomic Potential (EDIP).
Abstract: We calculate the free energies of unstable stacking fault (USF) configurations on the glide and shuffle slip planes in silicon as a function of temperature, using the recently developed Environment Dependent Interatomic Potential (EDIP). We employ the molecular dynamics (MD) adiabatic switching method with appropriate periodic boundary conditions and restrictions to atomic motion that guarantee stability and include volume relaxation of the USF configurations perpendicular to the slip plane. Our MD results using the EDIP model agree fairly well with earlier first-principles estimates for the transition from shuffle to glide plane dominance as a function of temperature. We use these results to make contact to brittle-ductile transition models.
TL;DR: In this paper, a detailed study of the first and second-order Raman scattering in wurtzite GaN and AlN at room and liquid helium temperatures is presented.
TL;DR: In this paper, a morphological prediction of the polar crystal morphology of the molecular ionic solid sodium chlorate is presented using interatomic potential calculations that employ surface-specific attachment energy calculations associated with an ab initio calculation of surface charges via a Hartree−Fock calculation using periodic boundary conditions.
Abstract: A morphological prediction of the polar crystal morphology of the molecular ionic solid sodium chlorate is presented. This prediction uses interatomic potential calculations that employ surface-specific attachment energy calculations associated with an ab initio calculation of surface charges via a Hartree−Fock calculation using periodic boundary conditions. The data predicts assignment of the absolute polarity of the crystal with respect to the published crystal structure (Burke-Laing, M. E.; Trueblood, K. N. Acta Crystallogr. 1977, B33, 2698), which reveals the chlorate-rich {−1 −1 −1} to be the observed form rather than its sodium-rich Freidel opposite, {111}. The predicted crystal morphology is in reasonable agreement with observed morphologies, although there is an underestimation of the dominant {200} form. The latter is rationalized with experimental data in terms of a face-specific solvent binding model.
TL;DR: In this paper, potential parameters for molecular dynamics simulations in the K2O-Na2O -CaO-MgO-Al2O3-SiO2 system were evaluated and applied successfully to reproduce the cell parameters and the symmetries of 25 crystals at 300K and 1 atm and the thermal behaviour of plagioclase feldspar.
Abstract: Potential parameters for molecular dynamics (MD) simulations in the K2O–Na2O–CaO–MgO–Al2O3–SiO2 system were newly evaluated and applied successfully to reproduce the cell parameters and the symmetries of 25 crystals at 300K and 1 atm and the thermal behaviour of plagioclase feldspar.
TL;DR: In this paper, an analytical model of the invariants (trace and anisotropy) of the diatom polarizability tensor is formulated that differ from existing models by the suppression of the classical long-range components at close range (damping).
Abstract: Analytical models of the invariants (trace and anisotropy) of the diatom polarizability tensor are formulated that differ from existing models by the suppression of the classical long-range components at close range (“damping”). Such damping is imperative in diatomic systems where the long-range polarizability terms are relatively large and/or the collision energies are high so that substantial penetration of the electronic shells of the colliding atoms takes place, e.g., for collision-induced light scattering by mercury vapor at high temperatures. When a small number of physically meaningful parameters of the polarizability models are properly adjusted, the binary trace and anisotropy collision-induced spectra of mercury vapor are closely reproduced from theory in all details. An improved model of the Hg–Hg interaction potential, which reproduces the existing bound mercury dimer states as well as the viscosity data, includes a similar damping term for suppression of the dispersion part at close range.
TL;DR: In this article, the molecular dynamics simulation in SrTiO 3 using the partially ionic model (PIM) was performed, and the relevant potential parameters except for the effective charge of each ion were optimized.
TL;DR: In this paper, the authors used a many-body interaction potential based on the embedded atom method to study multilayer atomic relaxations and local thermodynamic properties around the steps on Cu(410) and found that the step atoms relax at an angle of 38.6° with respect to the terrace normal.
TL;DR: In this paper, a posteriori corrections for electron correlation derived from density-functional theory have also been evaluated, and the agreement of the correlation-corrected values with available experimental data is very good.
Metz1
TL;DR: In this paper, the authors extended the hybridized mean spherical approximation integral equation to calculate the pair correlation function for krypton, beyond the critical isotherm, by using the two and three-body contributions to the interatomic potential.
Abstract: The formalism of the hybridized mean spherical approximation integral equation is extended to calculate the pair correlation function for krypton, beyond the critical isotherm, by using the two- and three-body contributions to the interatomic potential. The calculations are intended to examine the change of the pair correlation function caused by the inclusion of the Axilrod-Teller triple-dipole potential. It is seen that the three-body interaction cannot be ignored and that their effects become more significant for intermediate densities. In addition, a good agreement is found with the recent small-angle neutron-scattering experiments of Formisano et al. [Phys. Rev. Lett. 79, 221 (1997)].