Showing papers on "Interatomic potential published in 2001"
TL;DR: Empirical potential structure refinement (EPSR) is a method for developing a structural model of a liquid for which diffraction measurements are available as mentioned in this paper. But it is not suitable for water.
Abstract: Empirical potential structure refinement (EPSR) is a method for developing a structural model of a liquid for which diffraction measurements are available. The EPSR technique involves refining a starting interatomic potential energy function in a way that produces the best possible agreement between the simulated and measured site-site partial structure factors. Here a series of test simulations are performed to establish how well the EPSR method can recover the interatomic potential for a single component fluid of Lennard-Jones particles, and for a binary fluid consisting of charged atoms interacting at short range by a Lennard-Jones potential. Special attention is given to the problem of developing an accurate interatomic potential for water using these procedures. An alternative method for perturbing the starting potential is used to obtain the best possible fit to the diffraction data. The resulting parametrization of the water potential is in contrast to many existing effective potentials for water, ...
255 citations
TL;DR: In this paper, a block of linearly isotropic, plane-stress elastic solid consisting of a two-dimensional triangular atomic lattice with pair interatomic potential is loaded by constant shear velocities along the boundary and a pre-existing notch is introduced to represent an initial crack which starts to grow at a critical time after the loading process.
Abstract: Mechanisms of intersonic crack propagation along a weak interface under shear dominated loading are studied by both molecular dynamics and continuum elastodynamics methods. Part of the objective is to test if continuum theory can accurately predict the critical time and length scales observed in molecular dynamics simulations. To facilitate the continuum-atomistic linkage, the problem is selected such that a block of linearly isotropic, plane-stress elastic solid consisting of a two-dimensional triangular atomic lattice with pair interatomic potential is loaded by constant shear velocities along the boundary. A pre-existing notch is introduced to represent an initial crack which starts to grow at a critical time after the loading process begins. We observe that the crack quickly accelerates to the Rayleigh wave speed and, after propagating at this speed for a short time period, nucleates an intersonic daughter crack which jumps to the longitudinal wave speed. The daughter crack emerges at a distance ahead of the mother crack. The challenge here is to test if a continuum elastodynamics analysis of the same problem can correctly predict the length and time scales observed in the molecular dynamics simulations. We make two assumptions in the continuum analysis. First, the crack initiation is assumed to be governed by the Griffith criterion. Second, the nucleation of the daughter crack is assumed to be governed by the Burridge–Andrew mechanism of a peak of shear stress ahead of the crack tip reaching the cohesive strength of the interface. Material properties such as elastic constants, fracture surface energy and cohesive strength are determined from the interatomic potential. Under these assumptions, it is shown that the predictions based on the continuum analysis agree remarkably well with the simulation results.
146 citations
TL;DR: In this article, a proton jump between neighboring oxygen atoms of the AlO4 tetrahedron, defines proton mobility in an unloaded catalyst, and the potential energy surface is described by the QM-Pot method.
Abstract: Ab inito predictions of the proton-transfer reaction rates in chabazite, faujasite, and ZSM-5 zeolites are presented. The reaction studied, a proton jump between neighboring oxygen atoms of the AlO4 tetrahedron, defines proton mobility in an unloaded catalyst. Classical transition state theory is applied, and the potential energy surface is described by the QM-Pot method. The latter combines a quantum mechanical description of the reaction site with an interatomic potential function description of the periodic zeolite lattice. At room temperature, the calculated rates vary over a broad range of 10-6 to 105 s-1, depending on the zeolite type and the particular proton jump path within a given zeolite. Proton tunneling effects appear to be negligible above room temperature. The calculated reaction barriers vary between 52 and 106 kJ/mol. While in all three zeolites both low and high barriers exist, the special structural features of the zeolite frameworks allow the prediction that the proton mobility is gene...
134 citations
TL;DR: In this paper, a new SW-type potential set was developed for Si-O-F and Si-Cl systems based on interatomic potential energy data obtained from ab initio quantum-mechanical calculations.
Abstract: Stillinger–Weber (SW)-type potential sets have been developed for Si–O–F and Si–O–Cl systems based on interatomic potential energy data obtained from ab initio quantum-mechanical calculations. We have constructed the new potential sets in such a way that the obtained potentials are supersets of existing well-known SW-type potentials for Si, SiO2, and Si-halogen systems. Our aim of the potential development is to perform molecular dynamics (MD) simulations for both silicon and silicon dioxide etching by F or Cl on the same footing. Presented in this article are details of the potential derivation and some sample MD simulation results.
73 citations
TL;DR: In this article, the stability of the intermetallics Gd(Fe, T)12 and the site preferences of the ternary 3d or 4d transition element T are investigated by using a series of interatomic pair potentials.
Abstract: The stability of the intermetallics Gd(Fe, T)12 and the site preferences of the ternary 3d or 4d transition element T are investigated by using a series of interatomic pair potentials, ΦFe-Fe(r), ΦFe-Gd(r), ΦFe-T(r), ΦT-T(r), ΦT-Gd(r), and ΦGd-Gd(r), for the first time. The calculated results show that adding either Cr, Mo, Ti, or V atoms makes the crystal cohesive energy of Gd(Fe, T)12 decrease markedly, proving that these atoms can stabilize Gd(Fe, T)12 with ThMn12 structure even though the GdFe12 crystal structure is itself metastable. The calculated lattice parameters are in good agreement with experiment. The amount of cohesive energy decrease is correlated with the species and occupation site of the ternary atoms. The order of site preference of these stabilizing elements T is 8i, 8j, and 8f, with 8i corresponding to the greatest energy decrease. The calculated results further show that the addition of Co, Cu, Ni, Sc, and Zn does not stabilize the GdFe12 phase in the ThMn12 structure. The calculated results reported correspond well to available experimental data indicating that the ab initio interatomic potentials can be used to describe rare-earth materials.
71 citations
TL;DR: In this article, the potential energy curve of the ground electronic state of the Hg dimer has been calculated using the CCSD(T) procedure and relativistic effective core potentials.
Abstract: The potential energy curve of the ground electronic state of the Hg dimer has been calculated using the CCSD(T) procedure and relativistic effective core potentials. The calculated binding energy (0.047 eV) and equilibrium separation (3.72 A) are in excellent agreement with experiment. A variety of properties, including the second virial coefficient, rotational and vibrational spectroscopic constants, and vibrational energy levels, have been calculated using this interatomic potential and agreement with experiment is good overall.
48 citations
TL;DR: In this article, the authors used the reverse Monte Carlo method to interpret the results of molecular dynamics calculations and showed that simple repulsive interatomic potential models are suitable for describing the most important structural features qualitatively.
Abstract: Neutron diffraction measurements have been carried out for determining the total structure factor of liquid CCl4, SiCl4, GeCl4, TiCl4, VCl4, and SnCl4. The data were interpreted using the reverse Monte Carlo method, where the procedure started from results of molecular dynamics calculations. It is demonstrated that simple repulsive interatomic potential models are suitable for describing the most important structural features qualitatively. Based on detailed analyses of particle configurations, it is shown that “corner-to-face” type near-neighbor arrangements, that have been promoted for the interpretation of these structures over the last 20 years, are actually very rare, their occurrence being around 5% only. Instead, the dominance of “corner-to-corner” type orientational correlations is found.
47 citations
TL;DR: In this article, a new type of interatomic potential, based on the angular overlap model, has been developed in order to model compounds containing nonspherical transition metal ions, which has been implemented within the computational package GULP.
Abstract: A new type of interatomic potential, based on the angular overlap model, has been developed in order to model compounds containing “nonspherical” transition metal ions. The parametrized function has been implemented within the computational package GULP. We present full details of the energy and analytical derivatives, as well as the symmetry adaptation of the algorithms. The model has been successfully applied to LaMnO3 and Mn2O3, with the Mn-O bond distances within the MnO6 octahedra and the lattice parameters being reproduced to within 0.33% of those determined experimentally. Both the short-ranged repulsive potential and our new potential parameters were empirically fitted to reproduce the former structure and then successfully transferred to model the latter without modification.
43 citations
TL;DR: In this paper, lattice dynamics calculations of various microscopic and macroscopic phonon properties of the aluminosilicate garnets pyrope, grossular, and spessartine were performed using a transferable interatomic potential based on a shell model.
Abstract: This paper reports lattice dynamics calculations of various microscopic and macroscopic phonon properties of the aluminosilicate garnets pyrope, grossular, and spessartine (given by ${M}_{3}{\mathrm{Al}}_{2}{\mathrm{Si}}_{3}{\mathrm{O}}_{12},$ where $M=\mathrm{Mg},$ Ca, and Mn, respectively) using a transferable interatomic potential based on a shell model. These studies are fairly involved as these garnets have complex crystal structures with 80 atoms/primitive cell. The calculations have provided a theoretical understanding of the elastic constants, equation of state, phonon dispersion relations, and density of states of these materials. The computed density of states is used to derive various macroscopic thermodynamic quantities like the specific heat, thermal expansion, and mean-square atomic displacements. The computed phonon dispersion relations and total and partial densities of states have been particularly useful in interpreting the inelastic neutron-scattering data reported in the literature and the calculated results are found to be in good agreement with available experimental data. These studies have enabled a microscopic understanding of the variations in the phonon spectra of these materials and their manifestations in various macroscopic thermodynamic properties.
42 citations
TL;DR: In this paper, the CCSD(T)/aug-cc-pVQZ method has been employed to obtain accurate interatomic potentials for Li + He, from which spectroscopic parameters are derived.
41 citations
TL;DR: This study provides an insight into the nature of metastable modifications of crystal structures and the ways in which they are formed and indicates the existence of a critical bonding distance, above which interatomic interactions cannot be considered as bonding.
Abstract: Using theoretical simulations based on density functional theory within the generalized gradient approximation, a series of metastable phase transitions occurring in low-pressure Al2SiO5 polymorphs (andalusite and sillimanite) are predicted; similar results were obtained using semiclassical interatomic potentials within the ionic shell model. Soft lattice modes as well as related structural changes are analysed. For sillimanite, an isosymmetric phase transition at ca 35 GPa is predicted; an incommensurately modulated form of sillimanite can also be obtained at low temperatures and high pressures. The high-pressure isosymmetric phase contains five-coordinate Si and Al atoms. The origin of the fivefold coordination is discussed in detail. Andalusite was found to transform directly into an amorphous phase at ca 50 GPa. This study provides an insight into the nature of metastable modifications of crystal structures and the ways in which they are formed. Present results indicate the existence of a critical bonding distance, above which interatomic interactions cannot be considered as bonding. The critical distance for the Si—O bond is 2.25 A.
TL;DR: In this paper, the collision-induced absorption spectra in the infrared of the He-H pair were calculated using a rigorous quantum mechanical formalism, for a given temperature and frequency, the ratio of the absorption coefficient and the product of the H and He densities can be evaluated in seconds, even on small computers (e.g., PCs).
Abstract: On the basis of recent state-of-the-art ab initio calculations of the interatomic potential and dipole surface of interacting helium (He) and hydrogen (H) atoms, we calculate the collision-induced absorption spectra in the infrared of the He-H pair, using a rigorous quantum mechanical formalism. Furthermore, we present a simple analytical model which is capable of reproducing these calculated spectra with precision, for frequencies from 50 to roughly 10,000 cm-1 and temperatures from 1500 to 10,000 K. For a given temperature and frequency, the ratio of the absorption coefficient and the product of the H and He densities may be evaluated in seconds, even on small computers (e.g., PCs), provided this ratio exceeds a certain (very small) lower numerical limit.
TL;DR: In this article, a first-principle calculation based on density functional theory and the local density approximation (LDA) was employed to probe the extent of interatomic forces in aluminium caused by a variety of defect types.
Abstract: A computationally efficient and accurate description of interatomic interactions is indispensable to the fidelity of atomistic simulations. In the development of popular empirical potentials, it is assumed that atoms separated beyond a certain cut-off distance have negligible interatomic forces and hence may be safely ignored in the force calculations. This arbitrary, and yet common, practice of force truncation is undoubtedly ad hoc and is not grounded in the physics of the interactions. With the advent of fast computers and accurate first-principles calculations, it is now feasible to determine what this cut-off distance should be. In this work, employing a first-principles calculation based on density functional theory and the local density approximation (LDA) we probe the extent of interatomic forces in aluminium caused by a variety of defect types. The forces on neighbours to these defects, obtained from first-principles calculations, were then compared with the corresponding values from man...
TL;DR: In this article, diffusion Monte Carlo calculations of D 2 adsorbed inside a narrow carbon nanotube are presented, and the one-dimensional D 2 equation of state is reported.
Abstract: We present diffusion Monte Carlo calculations of D 2 adsorbed inside a narrow carbon nanotube. The one-dimensional D 2 equation of state is reported, and the one-dimensional character of the adsorbed D 2 is analyzed. The isotopic dependence of the constitutive properties of the quantum fluid are studied by comparing D 2 and H 2 Quantum effects due to their different masses are observed both in the energetic and the structural properties. The influence of the interatomic potential in one-dimensional systems is also studied by comparing the properties of D 2 and 4 He which have nearly the same mass but a sizeably different potential. The physics of molecular hydrogen adsorbed in the interstitial channels of a bundle of nanotubes is analyzed by means of both a diffusion Monte Carlo calculation and an approximate mean-field method.
TL;DR: Proukakis et al. as mentioned in this paper extended an earlier quantum kinetics treatment for dilute, weakly interacting, partially Bose-Einstein condensed gases, by consistently treating the dynamics of the uncondensed atoms to the same level of approximation as the condensed atoms.
Abstract: This paper extends an earlier quantum kinetics treatment for dilute, weakly interacting, partially Bose-Einstein condensed gases, presented by the author elsewhere (Proukakis N P and Burnett K 1996 J. Res. Natl Inst. Stand. Technol. 101 457), by consistently treating the dynamics of the uncondensed atoms to the same level of approximation as the condensed atoms. Our method is based on a hierarchy of coupled equations of motion for the condensate mean field and fluctuations around this mean field, truncated to second order in the (effective two-body) interatomic potential, and with suitable decoupling approximations for higher-order correlations. By applying perturbation theory in the Hartree-Fock-Bogoliubov basis, we re-derive the quantum kinetic theory of Walser et al (Walser R, Williams J, Cooper J and Holland M 1999 Phys. Rev. A 59 3878), which further indicates the consistency of our treatment with the Kadanoff-Baym non-equilibrium Green function formalism for trapped gases.
01 Dec 2001-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the structure, energy, and multiplicity of kinks on an a /2 〈111〉 screw dislocation in bcc Ta were studied in detail via atomistic computer simulation, using quantum-based multi-ion interatomic potentials derived from model generalized pseudopotential theory (MGPT) together with a robust Green's function simulation technique.
Abstract: The structure, energetics, and multiplicity of kinks on an a /2 〈111〉 screw dislocation in bcc Ta have been studied in detail via atomistic computer simulation, using quantum-based multi-ion interatomic potentials derived from model generalized pseudopotential theory (MGPT) together with a robust Green's function simulation technique. The stable core structure of the rigid screw dislocation is predicted to be weakly polarized and spread out on three {110} planes in 〈112〉 directions, with two energetically equivalent configurations. This double degeneracy leads to the possibility of anti-phase defects forming on the dislocation line as well multiple kinks and kink pairs. The zero-stress formation energies of 16 possible kink-pair configurations for bcc Ta have been calculated and are in the range 0.67–1.84 eV. The lowest kink-pair energy of the perfect screw is in good agreement with the best current empirical estimate. Under an applied stress, the corresponding kink–kink interaction energy displays a λ −1 elastic attraction when the separation λ is larger than 7 b =20 A, while the stress needed to maintain the kink pair varies as λ −1.5 .
TL;DR: In this article, structural properties of amorphous silicon (a-Si) have been examined by molecular-dynamics calculations using the Tersoff interatomic potential, and it was confirmed that computer-generated atomic configurations reproduce well the structural and dynamical properties of a-Si obtained experimentally.
Abstract: Structural characteristics of amorphous silicon (a-Si) have been examined by molecular-dynamics calculations using the Tersoff interatomic potential. It was confirmed that the computer-generated atomic configurations reproduce well the structural and dynamical properties of a-Si obtained experimentally. The a-Si networks contained two types of structural defect: threefold coordinated Si atoms (dangling bonds) and fivefold coordinated ones (floating bonds). The average bond length increased with the coordination number. Bond angles were distributed around 120° for the threefold coordinations, suggesting the existence of the atomic clusters constructed by sp2 bonding. On the other hand, they had peaks at ~60° and 90° for the fivefold coordinated atoms. Partial radial distribution functions revealed that the floating bonds have a tendency to cluster in the a-Si network.
TL;DR: In this paper, the Peierls model for dislocations is properly generalised to 2D, and it is possible to obtain a realistic description of dislocation cores with planar extension.
TL;DR: In this article, the authors determined the thermal equation of state (EOS) of MgSiO3 perovskite using the nonempirical variational induced breathing (VIB) interatomic potential with molecular dynamics simulations at pressures and temperatures of the lower mantle.
Abstract: The composition of the lower mantle can be investigated by examining densities and seismic velocities of compositional models as functions of depth. In order to do this it is necessary to know the volumes and thermoelastic properties of the compositional constituents under lower mantle conditions. We determined the thermal equation of state (EOS) of MgSiO3 perovskite using the nonempirical variational induced breathing (VIB) interatomic potential with molecular dynamics simulations at pressures and temperatures of the lower mantle. We fit our pressure-volume-temperature results to a thermal EOS of the form P(V, T) = P0(V, T0) + ΔPth(T), where T0 = 300 K and P0 is the isothermal Universal EOS. The thermal pressure ΔPth can be represented by a linear relationship ΔPth = a + bT. We find V0 = 165.40 A3, KT0 = 273 GPa, KT0′ = 3.86, a = −1.99 GPa, and b = 0.00664 GPa K−1 for pressures of 0–140 GPa and temperatures of 300–3000 K. By fixing V0 to the experimentally determined value of 162.49 A3 and calculating density and bulk sound velocity profiles along a lower mantle geotherm we find that the lower mantle cannot consist solely of (Mg,Fe)SiO3 perovskite with XMg ranging from 0.9–1.0. Using pyrolitic compositions of 67 vol % perovskite (XMg = 0.93–0.96) and 33 vol % magnesiowustite (XMg = 0.82–0.86), however, we obtained density and velocity profiles that are in excellent agreement with seismological models for a reasonable geotherm.
TL;DR: In this article, the authors adopt the lattice inversion method in acquiring the interatomic potentials related to rare-earth and transition metals and characterizes the site occupancies of Fe and Co in Y(Co,Fe)5, Y2Co, Fe 17, Y3Co,Co,M)29, and YTi(Fe,Co)11 by combining these potentials with computer simulation.
TL;DR: In this paper, the liquid-vapor coexistence curves for several interatomic potentials were calculated by the NpT plus test particle method and the structure of supercritical fluids in the process of expansion was investigated.
Abstract: We calculate the liquid–vapor coexistence curves for several interatomic potentials by the NpT plus test particle method. We also investigate the structure of supercritical fluids in the process of expansion. We find several universal properties irrespective of these potential types: (1) The law of rectilinear diameter is fulfilled. (2) The supercritical fluids expand inhomogeneously. (3) The coexistence curves scaled by the critical constants almost coincide with one another. As for a potential dependent property, we explain the behavior of the critical point systematically by using a quantity which characterizes the feature of attractive force.
15 Jul 2001-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the authors present calculations of screw dislocation cross slip in copper and nickel systems, using the nudged elastic band method and interatomic potentials based on the effective medium theory.
Abstract: This paper presents calculations of screw dislocation cross slip in copper and nickel systems, using the nudged elastic band method and interatomic potentials based on the effective-medium theory. The validity of recent attempts to predict cross slip activation energies by ‘elastic scaling’ between fcc metals is investigated, finding that reasonable predictions can be made using the approach suggested by Rasmussen [T. Rasmussen, Phil. Mag. A 80 (2000) 1291]. The experimentally determined cross slip activation energy and the minimum stable screw dislocation dipole height for copper are explained on the basis of cross slip of jogged screw dislocations.
TL;DR: In this article, a combination of First-Principles Density Functional Theory (DFT) and classical molecular dynamics with interatomic potential is used to examine bonding differences between two types of nanotube deformation: bending and pushing with atomically sharp AFM tips.
Abstract: A combination of First-Principles Density Functional Theory (DFT) and classical molecular dynamics with interatomic potential is used to examine bonding differences between two types of nanotube deformation: 1 bending, and 2 pushing with atomically sharp AFM tips Bent tubes maintain an all-hexagonal network up to large bending angles AFM-probed tubes, in contrast, display a more interesting behavior, which depends on the representation of the AFM tip
TL;DR: In this article, the core structure of dislocations with Burgers vector in NiAl was determined using the Peierls model generalised to 2D and compared with atomic computer simulations from the literature using an empirical EAM interatomic potential.
TL;DR: In this paper, the authors used Monte Carlo simulations in conjunction with a semi-empirical N -body potential to study the surface segregation at the (0, 0, 1) surface in Cu(Ag) alloys.
TL;DR: In this paper, the interaction of Ag+ ions with the ZSM-5 lattice was studied by means of a combined quantum mechanics/interatomic potential function method, and a new Ag(I)−O interaction potential was parametrized based on ab initio data and its quality was tested.
Abstract: The interaction of Ag+ ions with the ZSM-5 lattice was studied by means of a combined quantum mechanics/interatomic potential function method. A new Ag(I)–O interaction potential was parametrized based on ab initio data and its quality was tested. The Ag+ ions preferentially occupy the sites on the intersection of the main and zig-zag channels of ZSM-5. Ag–O distances in the range 2.32–2.36 A and coordination to two framework oxygen atoms were found, in good agreement with available EXAFS data. The interaction energies of Ag+ with zeolite (127–132 kcal mol−1 for sites on the channel intersection) are about 20 kcal mol−1 smaller than those found for the Cu+/ZSM-5 system. The calculated vertical excitation energies of the T1←S0 transition show a strong correlation
with the coordination number of the Ag+ ions. Since two-coordinated sites on the channel intersection are strongly preferred by the Ag+ ions only a single absorption peak is predicted for the Ag/ZSM-5 system, in agreement with experimental observation.
TL;DR: In this paper, experimental observation of multimodal angular distributions of 15-keV He 0 -atoms scattered under glancing angles from an Fe(0, 0, 1) surface along a [0, 0, 0] surface direction is reported.
TL;DR: In this paper, a semi-empirical many-body interatomic potential for Al was obtained in a previous work within the second-moment approximation to the tight-binding model.
Abstract: A semi-empirical many-body interatomic potential for Al was obtained in a previous work within the second-moment approximation to the tight-binding model. This was used, in tandem with molecular-dynamics simulations to study the self-diffusion of single adatoms on Al(1 0 0) and Al(1 1 1) surfaces. The diffusion coefficient in the case of Al/Al(1 0 0) system was computed. The latter presents Arrhenius behavior. The migration energies and pre-exponential factors for both hopping and exchange mechanisms were determined as well. It was found that the hopping mechanism is dominant for temperatures below 800 K. Furthermore, our results for the migration energy of Al on Al(1 1 1) are in good agreement with recent experimental data. There is, however, an important discrepancy for the pre-exponential factor. The temperature dependence of the relaxation of the adatoms was also obtained for both the (1 0 0) and (1 1 1) surfaces. The (1 1 1) surface was found to have a stronger temperature dependence.
TL;DR: In this paper, the excitation spectrum of the A0 + (5 3 P 1 )← X0+ (5 1 S 0 ) transition in the CdHe van der Waals molecule has been recorded in an experiment of a continuous supersonic molecular beam crossed with a pulsed dye laser beam.
TL;DR: The results of atomistic simulations of migration and formation energies of mono-and di-vacancies in bulk tungsten are presented in this paper, where a stochastic molecular dynamics using a generalized simulated annealing procedure is employed.
Abstract: The results of atomistic simulations of migration and formation energies of mono- and di-vacancies in bulk tungsten are presented in our paper. The interatomic potential for tungsten was extracted with the recursive procedure from ab initio calculations of the cohesive energy. A stochastic molecular dynamics using a generalized simulated annealing procedure was employed in the simulations. Calculated values of mono- and di-vacancies energy parameters are in a good agreement with experimental data and with the results of other calculations.