On the Kinetic Theory of Dense Fluids. XV. Some Comments on the Rice—Allnatt Theory

In this paper it is shown that, within the framework of the Rice—Allnatt theory of transport phenomena in simple dense fluids, the cross-correlation functions of the soft and hard forces are exactly zero. A relation is found between the soft doublet and soft singlet friction coefficients, and an approximate theory is developed for the soft components of the shear viscosity and the thermal conductivity. The main assumption in this approximation is that of small step diffusion. The soft doublet friction coefficient which is derived in the first part of the paper is then used to calculate values for the soft force contribution to the viscosity and thermal conductivity. It is shown that the equilibrium properties of simple liquids are not known with sufficient accuracy to allow a complete test of the R—A theory, but that the expressions in this theory seem to be moderately insensitive to the equilibrium properties used.