Ronald A. Aziz

An accurate intermolecular potential for helium

A simple realistic and precise empirical intermolecular potential is proposed for helium. It possesses nearly the correct Hartree–Fock repulsion as well as the correct long range behavior. It was fitted to recent accurate intermediate temperature second virial coefficients and thermal conductivity data as well as high temperature viscosity values. It is able to predict second virial coefficients over an extended temperature range from 1.5 to 1475 K. Above 100 K it reproduces substantially all of the transport properties to within experimental error in a manner superior to all other potentials in existence. Below 100 K where the transport data are less reliable, it produces a good representation of the isotopic differences in the viscosity. It also predicts differential cross sections reasonably well. In spite of a few remaining discrepancies, when all the different macroscopic properties are considered, the potential produces the best representation of the helium interaction available at this time.

Empirical Equations to Calculate 16 of the Transport Collision Integrals Ω(l, s)* for the Lennard‐Jones (12–6) Potential

We have calculated 16 of the reduced transport collision integrals Ω(l, s)* as a function of reduced temperature T* for the Lennard‐Jones (12–6) potential. These calculations are more accurate than those of Hirschfelder, Curtiss, and Bird, which are frequently used. Empirical equations are presented which allow the calculation of the collision integrals for any reduced temperature in the range 0.3≤ T*≤ 100 without interpolation from tables. The error in the values so obtained is probably less than 0.1%.

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.

A new determination of the ground state interatomic potential for He2

A simple accurate potential of the HFD-B form, which appears to be the best characterization of the He-He interaction constructed to date, is presented. It has been fitted to low temperature second virial coefficient data and recent accurate room temperature viscosity data, while at the same time pinning the repulsive wall to the value calculated by Ceperley and Partridge at 1 Bohr. It possesses a well depth of 10·948 K, considerably deeper than many of the recent empirical or ab initio potentials. It reproduces, within experimental error, such dilute gas properties as second 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 integral cross sections and backward glory oscillations in the integral cross sections. Finally, it accounts for nuclear magnetic relaxation in 3He and supports a weakly bound state in the 4He interaction.

An accurate intermolecular potential for argon

A potential function for ArKr is derived which is able to reproduce the best data available for the differential and the integral cross section, the second virial coefficient and the diffusion and viscosity within the quoted experimental errors.

A highly accurate interatomic potential for argon

A modified potential based on the individually damped model of Douketis, Scoles, Marchetti, Zen, and Thakkar [J. Chem. Phys. 76, 3057 (1982)] is presented which fits, within experimental error, the accurate ultraviolet (UV) vibration‐rotation spectrum of argon determined by UV laser absorption spectroscopy by Herman, LaRocque, and Stoicheff [J. Chem. Phys. 89, 4535 (1988)]. Other literature potentials fail to do so. The potential also is shown to predict a large number of other properties and is probably the most accurate characterization of the argon interaction constructed to date.

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.

An accurate potential energy curve for helium based on ab initio calculations

Korona, Williams, Bukowski, Jeziorski, and Szalewicz [J. Chem. Phys. 106, 1 (1997)] constructed a completely ab initio potential for He2 by fitting their calculations using infinite order symmetry adapted perturbation theory at intermediate range, existing Green’s function Monte Carlo calculations at short range and accurate dispersion coefficients at long range to a modified Tang–Toennies potential form. The potential with retardation added to the dipole-dipole dispersion is found to predict accurately a large set of microscopic and macroscopic experimental data. The potential with a significantly larger well depth than other recent potentials is judged to be the most accurate characterization of the helium interaction yet proposed.

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.