Showing papers on "Interatomic potential published in 1979"
TL;DR: In this article, high-resolution, differential collision cross section data for the scattering of He by Ar atoms, obtained in Gottingen, are found to be inconsistent with the predictions derived from a recently proposed He-Ar potential.
Abstract: New, high resolution, differential collision cross section data for the scattering of He by Ar atoms, obtained in Gottingen, are found to be inconsistent with the predictions derived from a recently proposed He–Ar potential [M. Keil et al., J. Chem. Phys. 70, 482 (1979)] and confirm previous work by K. M. Smith et al. [J. Chem. Phys. 67, 152 (1977)]. It is shown that the He–Ar well depth is 29.4 K (accurate to 5% and 44% larger than the value of Keil et al.), independent of the parametrization of the potential. A careful analysis of the bulk properties of the He–Ar mixture also shows that the attractive part of the potential proposed by Keil et al. is too weak. A potential of the SPFD form is presented which is able to reproduce the best data for the differential cross section, the second virial coefficient, the diffusion and viscosity within the quoted experimental errors.
66 citations
TL;DR: In this paper, a complete account of the application of the principles of bifurcation analysis for general materials to the particular case of cubic crystals subjected to hydrostatic loading is presented.
Abstract: A complete account is presented of the application of the principles of bifurcation analysis for general materials to the particular case of cubic crystals subjected to hydrostatic loading. The treatment of crystal stability is classical in that (i) the loading environment is fully specified, to sufficient order and in both its active and passive modes, and (ii) the potential energy of the system as a whole is examined in all the nearby, possibly inhomogeneous, configurations allowed by the kinematic constraints. Computations are made of the pressures and the bulk and shear moduli of the entire Morse-model family of fcc, bcc, and sc monatornic crystals under pure hydrostatic compression and tension. The stable range of each lattice as well as the potential bifurcations at the range limits are presented and discussed in terms of the role of the particular lattice structure and the effective range of the interatomic potential function (as specified by the parameter log β). The fee lattices are stable in compression and in tension up to an all-round stretch λ = Λk, at which point the bulk modulus vanishes; Λk, is a monotonically decreasing function of log β. The bcc lattices are stable for λ < ΛCR, where the bulk modulus or the shear modulus μ vanishes (depending upon the value of log β) at λ = ΛCR. For very large values of log β a second range of bcc stability is located in a region of hydrostatic expansion. The sc crystals are stable only in a range of hydrostatic tension and only for relatively short-range interatomic interactions (large log β); the present work appears to be the first in which a theoretical range of stability of sc crystals has been revealed. The question of the possibility of assessing lattice stability under load with the aid of higher order moduli at zero load is given consideration quantitatively for the fee lattices and the bcc lattices that are stable at zero load. Finally, the present approach to crystal stability is distinguished from some simplistic notional criteria based upon local convexity of strain energy and, for the Morse-model cubic crystals, quantitative comparisons are made with the present classical treatment of stability in a hydrostatic environment.
49 citations
TL;DR: In this paper, the atom-atom potentials for carboxylic acids were derived by making a least-squares fit to interaction energies, calculated by the ab initio MO-SCF method.
Abstract: Atom-atom potentials for carboxylic acids have been derived by making a least-squares fit to interaction energies, calculated by the ab initio MO-SCF method. Energies for 12 configurations of the f...
46 citations
TL;DR: In this article, the ground and first excited electronic states of the weakly bound molecule NaAr and the first excited state of NaNe were derived by inverting spectral data to analytic potential functions.
Abstract: The interatomic potential functions for the ground and first excited electronic states of the weakly bound molecule NaAr and the first excited state of NaNe are derived by inverting spectral data to analytic potential functions. Using the Thakkar potential expansion, it is shown how one may deduce vibrational assignments, compute accurate dissociation energies, and combine two potentials with an atomic transition to advantage. The resulting potential functions are in excellent agreement not only with spectroscopic data, but also with potentials derived from scattering and atomic resonance line broadening experiments.
41 citations
TL;DR: In this paper, the properties of solitary waves in a three-dimensional, monatomic, face-centered cubic lattice are studied and the equations of motion for the atoms are solved numerically using a computer-molecular-dynamic technique.
Abstract: : The properties of solitary waves in a three-dimensional, monatomic, face-centered cubic lattice are studied. The atoms of the lattice are assumed to interact via a Morse-type interatomic potential. For the discrete lattice, the equations of motion for the atoms are solved numerically using a computer-molecular-dynamic technique and, from their solution, the stability of the waves investigated. It is pointed out that the solitary waves are fairly stable to longitudinal planar oscillations, somewhat less stable to mutual collisions, and still less stable to transverse planar oscillations. It is also observed that under some conditions coupled longitudinal and transverse solitary waves can propagate in phase with the same propagation velocity in the lattice. The equations of motion are then derived in the long-wavelength, continuum limit and studied in some detail. A comparison of their solutions is made with the results for the discrete-lattice model and it is shown that the continuum equations are capable of predicting many of the same effects.
28 citations
TL;DR: In this article, an ESMSV potential for the NeNe interaction has been obtained from a simultaneous fitting to scattering, gaseous and solid state data, considering experimental differential cross sections at three different collision energies, total absolute cross sections measured in the thermal energy range, experimental second virial coefficients in the 40-1000 K temperature range, and the cohesion energy of solid neon at 0 K.
23 citations
TL;DR: Several variants of the Gordon-Kim method are tested by comparing the calculated interatomic potentials of homonuclear inert-gas atoms with experiment as discussed by the authors, and it is concluded that two variants, the first due to Lloyd and Pugh and the second to Clugston, both of which use the dispersion series at long range, are the most reliable.
20 citations
TL;DR: In this article, a modified Kramers-Kronig analysis was used to study the self-broadening of the 253.65 nm mercury resonance line at high vapor density (2.7 × 10 19 −2 ).
Abstract: Reflection techniques are used to study self-broadening of the 253.65 nm mercury resonance line at high vapor density (2.7 × 10 19 −2.7 × 10 21 atoms-cm -3 ). The absorption profiles are deduced from reflectance data using a modified Kramers-Kronig analysis. Another method, based on semi-classical dispersion theory, is shown to be inadequate and is used here only in order to compare our results with previously reported values. Conclusions are stated concerning the effects of different kinds of forces, broadening rate, oscillator strength, and interatomic potential curves with the help of the available theoretical approaches for which validity ranges are discussed.
10 citations
TL;DR: In this article, the melting temperature at the mantle-core boundary may range between 3500 and 4300 K, while at the inner core-outer core boundary it might range between 4500 and 7000 K. The average melting temperature gradient is shown to be between 0.6 and 1.1 deg/km.
Abstract: Summary
The melting curve (melting temperature versus pressure) of iron is fundamental to an understanding of the physics of the Earth's core. Since experimental data are available for pressures a few orders of magnitude smaller than the core pressures, the problem is to find the correct ways of extrapolating them. Here we employ Ross’ melting criterion, a reformulation of Lindemann's law in the framework of statistical mechanics, because all the proposed empirical melting laws can be deduced from it; it also allows us to take into account the interatomic potential and the various crystal structures which iron may possess. The results of our calculations lead us to the conclusion that the melting temperatures of iron at the core pressures are extremely uncertain since no definite choice among possible potential functions is allowed. The melting temperature at the mantle–core boundary may range between 3500 and 4300 K, while at the inner core–outer core boundary it may range between 4500 and 7000K. The average melting temperature gradient is shown to be between 0.6 and 1.1 deg/km. The problem of establishing if the core is made of fcc or hcp iron is definitely secondary to that of the choice of the potential function.
8 citations
TL;DR: In this article, an extremely simplified interatomic potential proposed recently has been modified so that it satisfied the basic properties like charge neutrality and unit screening function at origin (φ(0)= 1).
Abstract: An extremely simplified inter-atomic potential proposed recently has been modified so that it satisfied the basic properties like charge neutrality and unit screening function at origin (φ(0)= 1). The simplicity is retained to a great extent so that it can still be used for calculations on charged particle propagation in real solids with defects.
8 citations
TL;DR: The basic physical problems of the geometric models and structural models of grain boundaries based on computer simulations are considered in this article, where the experimental and theoretical evidence indicated that grain boundary properties can, in general, not be derived from computer models, as these properties depend partially on electronic effects.
Abstract: The basic physical problems of the geometric models and structural models of grain boundaries based on computer simulations are considered. By comparing the approximations made in these models with the general solution of the problem based on the theory of metallic cohesion, we are led to conclude that
igeometric grain boundary models (coincidence models) may be used to derive certain geometric features of a boundary (e.g. the boundary periodicity). However, due to the fact that interatomic forces are neglected, it seems not possible to deduce the actual atomic structure and properties of grain boundaries on the basis of these models.
iiDislocation models of grain boundaries seem to be of physical significance only for low energy boundaries. In all other boundaries, misfit dislocation are theoretically and experimentally found to be delocalized in the sense that their core is smeared out in the plane of the boundary.
iiiStructural boundary models deduced by computing the minimum energy atomic configuration using pairwise interatomic potential functions seem to represent a reasonable approximation of the actual atomic structure.
ivThe experimental and theoretical evidence presented indicates that grain boundary properties can, in general, not be derived from computer models, as these properties depend partially on electronic effects.
vFurther developments of the physical understanding of grain boundaries seems to require the incorporation of electronic effects in the theory of interfaces.
TL;DR: In this article, it was shown how the asymptotic interatomic potential arises from a master equation approach, where the density matrix equation for the combined radiation and atoms is approximated by the radiation density matrix obtained by tracing over the states of the reservoir consisting of a dilute gas of atoms.
TL;DR: In this article, an intuitive approach is used to develop a theory of the transverse current correlation function in simple liquids, and the memory function obtained on the basis of this approach is expressed in terms of the velocity autocorrelation function for the kinetic part and the radial distribution function, the interatomic potential and a time-dependent term which describes the relative motion of two atoms in the liquid for the potential part.
Abstract: An intuitive approach is used to develop a theory of the transverse current correlation function in simple liquids. The memory function obtained on the basis of this approach is expressed in terms of the velocity autocorrelation function for the kinetic part and in terms of the radial distribution function, the interatomic potential and a time-dependent term which describes the relative motion of two atoms in the liquid for the potential part. The results for the memory function and the frequency spectrum are found to be in satisfactory agreement with the computer simulation studies of Levesque et al.
TL;DR: In this article, the equations of motion for longitudinal and transverse waves in a non-linear, dispersive three-dimensional elastic continuum and the conditions under which these waves retain their initial longitudinal or transverse character are obtained.
Abstract: The equations of motion for longitudinal and transverse waves in a non-linear, dispersive three-dimensional elastic continuum and the conditions under which these waves retain their initial longitudinal or transverse character are obtained. The equations of motion have the one-dimensional continuum form and hence the standing wave results described previously may be applied to the three-dimensional continuum. The example of the rare-gas solids is discussed. The analysis is based on a 6-12 interatomic potential and a FCC lattice. It is found that for the three symmetry directions 100, 110, 111 only the three longitudinal waves and one of the 110 transverse waves can retain their initial character and the standing-wave effects would be masked by acoustic damping above 1K in argon.
TL;DR: In this paper, two extreme models of a simple fluid are considered: the ideal gas in which the atoms are described simply by plane waves; in the second every atom is considered as harmonically coupled to the bubble within which it sits and the bubble systems is assumed in turn to form a free gas.
Abstract: Two extreme models of a simple fluid are considered. The first is the ideal gas in which the atoms are described simply by plane waves; in the second every atom is considered as harmonically coupled to the «bubble» within which it sits and the «bubble» systems is assumed in turn to form a free gas. Once a suitable soft-core interatomic potential has been chosen and a mixture of the two types of «fluid» has been considered, the single-particle potential is self-consistently determined. Then, by minimizing the system free energy, the distribution of the atomic population between the two «fluids» at thermodynamic equilibrium is found. Finally the various thermodynamic functions of the mixture are determined. The «two fluids» model is found to be actually practicable.
TL;DR: In this paper, the Brinkman potential is used for the numerical calculation of the classical deflection angle, and the results are compared with those obtained by the Leibfreid-Oen approximation of the same interatomic potential.
Abstract: The Brinkman potential is used for the numerical calculation of the classical deflection angle. The results are compared with those obtained by the Leibfreid-Oen approximation of the same interatomic potential. The discrepancy between the two results is pointed out also for large angle scattering.
01 Jan 1979
TL;DR: In this paper, a theoretical and experimental study of the influence of collisions on the saturation spectroscopy line shapes associated with three-level gas vapor systems was performed with the goal of gaining new information concerning the collisional processes that occur in atomic vapors, the nature of the interatomic potential between a ground state and an excited-state atom and the possibility of collision-induced enhancement of the absorption of radiation by an atomic system.
Abstract: We report on a theoretical and experimental study of the influence of collisions on the saturation spectroscopy line shapes associated with three-level gas vapor systems. The study is carried out with the goal of gaining new information concerning (a) the collisional processes that occur in atomic vapors, (b) the nature of the interatomic potential between a ground state and an excited-state atom and (c) the possibility of collision-induced enhancement of the absorption of radiation by an atomic system. In each of these areas, new results are obtained.