Intermolecular potentials that are functions of thermodynamic variables

Abstract

An expression is given for obtaining an effective intermolecular potential, which is a function of thermodynamic variables, by averaging over statistical variables that are not of interest. It arises in McMillan and Mayer's theory of solutions, but includes also the methods of taking orientational averages, of including weak three-body potentials in effective two-body potentials, of transcribing the grand partition function of a c-component system to one of a system of (c - 1) components, and is closely related to a generalization to an arbitrary set of molecules of the potential distribution theorem of the grand canonical ensemble.