Binary collisions in fluids: II: velocity auto correlation function

Abstract

A calculation based on the Zwanzig–Mori formalism and the binary collision expansion is presented for the velocity auto correlation function (VCF) of simple classical fluids. The binary collision expansion is truncated after the second term, thus incorporating exactly all the effects of a single collision between two particles, and this expansion is applied to the memory function associated with the VCF. The only inputs required are the pair distribution function g(r) and a central potential U(r). The potential chosen is the Lennard–Jones potential. It is seen that the approximation of the memory function by the binary force auto correlation function yields results for VCF that are in very good agreement with molecular dynamics results over a wide range of densities from dilute gases to liquids.