Exp-6 Cell Model Calculations for the Inert Gas Solids. II. Thermodynamic Properties—The Effect of the Triple-Dipole Term

Abstract

Using the potential parameters developed in Part I of this series of papers we now present a comparison of the theoretically predicted and experimentally measured thermodynamic properties of the four inert gas solids, neon, argon, krypton, and xenon. It is shown that without the inclusion of any three-body term the exp-6 potential gives a good prediction of most available data. The predicted data are sensitive to the inclusion of the three-body term, but its inclusion in the calculations removes the good agreement with experiment. Some discussion is given to the usefulness of the “effective pair additive” potential, for which the exp-6 is obviously a better choice than is the commonly accepted Lennard-Jones (12–6). The calculations further show that the prediction of the solid state properties using a cell model, and including the triple-dipole nonadditive term, can indicate the unacceptability of a pair potential which nevertheless is able to accurately predict second virial gas data. The exp-6 potential, when parameters are characterized from solid state data with the inclusion of the three-body term in the calculation, is only partially successful in the prediction of either second virial or solid state data but at least shows the likelihood of a pair potential being successful in these two greatly disparate tasks.