Analytical approximations to virial coefficients for pure and mixed systems

Abstract

Analytic approximations, in the form of finite polynomial expansions in T -1, are given to the pressure virial coefficients of pure Lennard-Jones systems with strictly pairwise-additive potentials. Results are given through fifth order in both two and three dimensions. These analytic forms are combined in Pade approximants for the compressibility factor in three dimensions, and the critical constants found from them are in agreement with those obtained elsewhere; equally good agreement is found in the two dimensional case. Also reported are calculations of two- and three-dimensional third virial coefficients of mixtures of the heavier rare gases and simple molecules. The interactions are represented by single centre models, Lennard-Jones potentials which are shown to give mixed second virial coefficients in reasonable agreement with experimental values. The calculated and experimental third virials do not agree, but the inclusion of three-body interactions, through the triple-dipole and related terms, imp...