A configuration relaxation model for transport processes in a monatomic liquid

Abstract

A model of transport processes in a monatomic liquid is proposed in which no assumption of the Brownian motion type is made about the statistical features of the molecular motion. Instead, the pair configuration distribution function is assumed to satisfy a relaxation equation. The model gives a good order of magnitude agreement with experiment for the shear viscosity, thermal conductivity, and self-diffusion coefficients of liquid argon, in terms of the relaxation time and its temperature derivative. The momentum correlation function is found to have the form of a decaying oscillation, and goes over in a natural way to the exponential decay characteristic of Brownian particles for the case of a heavy particle suspended in the liquid. This result supports a more general argument that the use of Fokker-Planck equations to describe the evolution of liquid molecular distribution functions cannot be justified by the conventional method of appealing to the ideas of Brownian motion theory. However, the possibility that equations of this type may be shown to be adequate approximations for liquid systems by a different formulation is not excluded.