Computer "Experiments" on Classical Fluids. IV. Transport Properties and Time-Correlation Functions of the Lennard-Jones Liquid near Its Triple Point

Abstract

A molecular-dynamics "experiment" was performed for a system of 864 particles interacting through a Lennard-Jones potential. The state considered was in the immediate neighborhood of the triple point. The total duration of the "experiment" was quite large: It corresponds to ${10}^{\ensuremath{-}9}$ sec in the case of argon. Transport coefficients were calculated using the standard Kubo formulas. They are compared with the prediction of a simple hard-sphere model. It is shown that, as in the case of the hard-sphere fluid near solidification, the Kubo-correlation function relative to the shear viscosity presents a tail extending at large time. The inclusion of this tail turns out to be essential in explaining the transverse-correlation function and the dynamical-structure factor, which shows, for the lowest wave vectors accessible in this study, a characteristic Brillouin doublet structure. Using the hydrodynamical model of Zwanzig and Bixon, it is shown that the introduction of the long-time tail in the Kubo-correlation function for the viscosity explains the negative plateau of the velocity-autocorrelation function observed near the triple point by Rahman and others.