M. J. Slaman

The argon and krypton interatomic potentials revisited

Accurate interatomic potentials are constructed which represent subtle but significant improvements for the argon and krypton interactions. The potentials are of the HFD-B form with definite advantages over the HFD-C form. These new potentials incorporate recent determinations of the C6 dispersion coefficient and accurately predict the best available spectroscopy, scattering and bulk data, some of which data were published after earlier constructions.

An examination of ab initio results for the helium potential energy curve

Obtaining a ground state potential energy curve for helium has been the subject of much research involving empirical, semiempirical, and ab initio methods. In this work, we examine critically recent ab initio potentials proposed for this interaction with respect to their ability to predict certain accurate experimental data. To accomplish this analysis, potentials with a modified HFD‐B form were fit to the recent theoretical work of van Duijneveldt and co‐workers [Vos, van Lenthe, and van Duijneveldt, J. Chem. Phys. 93, 643 (1990) and Vos, van Mourik, van Lenthe, and van Duijneveldt (to be published)] and Liu and McLean (LM‐2) [J. Chem. Phys. 91, 2348 (1989)]. A well depth (e/k=10.92 K) and a separation at the minimum (rm=2.9702 A) consistent with both determinations were chosen and the properties of helium were calculated based on these potentials. These ‘‘mimic’’ potentials fail to predict the very low temperature 4He and 3He virials and one of them [Vos, van Maurik, van Lenthe, and van Duijneveldt (to ...

The Ne-Ne interatomic potential revisited

Abstract The neon-neon interaction has been re-examined in the light of new data, both theoretical and experimental. Because of recent interest in solids at very high pressures, a new accurate potential is presented with particular interest paid to its highly repulsive region. A potential in HFD-B form incorporating the most recent dispersion coefficients was fitted to accurate viscosity data and high-energy scattering beam data. The potential is able to predict a wide range of macroscopic (second virial coefficients, viscosity, thermal conductivity, diffusion and 0 K binding energy) and microscopic properties (spectroscopic differential and high-energy total cross sections). The potential is extended to very short range by extrapolating to united atom perturbation results.

On the Xe-Xe potential energy curve and related properties

A simple accurate potential of the HFD-B form is presented which appears to be the best characterization of the Xe-Xe interaction to be constructed to date. It reproduces, within experimental error, such dilute gas macroscopic properties as virial coefficients, viscosities and thermal conductivities over a wide temperature range. It also predicts, within experimental error, such microscopic properties as differential cross sections, high energy beam data, the glory structure in the total cross sections and the vibrational spacings of the Xe dimer. Moreover, it predicts the binding energy of the solid at 0 K.

The repulsive wall of the Ar–Ar interatomic potential reexamined

The repulsive wall of the Ar–Ar interaction is reexamined with the purpose of rationalizing the apparent inconsistency between high energy beam results and high temperature transport data. A new piece‐wise experimental potential is proposed which predicts not only the beam results but a large set of transport data up to 7000 K. Lower temperature/energy data are predicted almost equally as well as other state‐of‐the‐art empirical potentials.

XC and HFD-B potential energy curves for Xe-Xe and related physical properties

Abstract The XC (exchange-Coulomb) and the HFD (Hartree-Fock-dispersion) potential models for the interaction of two closed shell atoms are reviewed briefly. It is shown that while the original XC potential model (XC-1) does not lead to an optimal potential for the Xe-Xe interaction, two variants, XC-2 and XC-3, do lead to optimal interaction energies for this interaction as a function of the interatomic distance R . The three XC potentials, two HFD-B type potentials, and three other literature potentials are compared with respect to their predictive ability for various microscopic and (dilute gas) macroscopic properties of Xe. One of the HFD-B potentials, developed here, is a modification of the original HFD-B potential for Xe-Xe and this HFD-B2 potential, and the XC-3 potential, are apparently the most reliable representations of the two-body Xe-Xe interaction available. The two-bodypotentials are also used to help discuss the problems associated with the representation of many-body interactions in rare gas systems.

Exchange-Coulomb potential energy curves for He-He, and related physical properties

The investigation of the reliability of the original simple overall damped form of the XC (exchange-Coulomb) potential is extended to the He-He interaction, and a new multidamped version of the XC potential is introduced. New one and two parameter overall damped, and one and two parameter multidamped XC potentials for He-He are constructed. The results obtained from these potentials for the second virial coefficients (1·4 < T < 623 K) and transport properties of dilute He gas, and for integral collision cross-sections for He-He collisions, are compared with experiment and with those obtained with the (reference) HFD-B2 potential. The various XC potentials are explicitly compared, over a wide range of interatomic distances R, with the HFD-B2 potential, with ab initio results and with a very accurate (R ⩽ 3a 0) quantum Monte Carlo potential. While the one parameter versions of the XC potentials generally yield very good results, the two parameter overall and individually damped XC potentials, and the HFD-B2...

Two‐ and three‐body forces in the interaction of He atoms with Xe overlayers adsorbed on (0001) graphite

In order to address the problem of three‐body interactions in gas–surface scattering, we considered the collision of a He atom with the (0001) surface of graphite coated by a monolayer of Xe. To eliminate the uncertainties connected with errors in the two‐body He–Xe interaction, we determined the latter by crossed‐beam differential collision cross‐section measurements performed at two energies (67.2 and 22.35 meV). These scattering data together with room‐temperature bulk diffusion data are then fitted with a Hartree–Fock–dispersion–type function to yield an interaction potential that explains most of the properties of this system within the experimental errors and represents an improvement on previously published He–Xe potentials. Helium diffraction measurements are then carried out from the Xe overlayer and the dependence of the specular intensity from the angle of incidence is carefully determined. Further, a He–surface potential is constructed by adding together the following terms: (1) the He–Xe pair...

Experimental determination of the refractivity virial coefficients of atomic gases

Values of the second refractivity virial coefficients BR of the atomic gases He, Ne, Ar, Kr, and Xe have been measured with a recently improved differential‐interferometric technique to a high degree of accuracy. This device basically consists of two coupled grating interferometers. One interferometer, with two similar cells in series, measures differentially the higher‐order effects of density while the second interferometer, with two similar cells in parallel, simultaneously measures the absolute value of the refractive index. In the range of pressure investigated (up to 40 MPa), the third refractivity virial coefficient CR becomes significant for the gases Ar, Kr, and Xe and the fourth refractivity virial coefficient DR becomes significant for Xe. The agreement between our experimental BR and the theoretical prediction based on the classical dipole–induced‐dipole model is fairly good for Ar, Kr, and Xe but poor for He and Ne. For He and Ne, however, good agreement is obtained when a semiclassical appro...

Simple accurate potentials for Ne-Kr and Ne-Xe

Recent literature potentials for Ne–Kr and Ne–Xe systems are analyzed and critically assessed as to their abilities to predict dilute gas bulk and microscopic properties. Two new potentials are proposed for the Ne–Kr and Ne–Xe interactions which accurately predict a large number of properties and appear to be the best characterizations of these interactions.