MOLECULAR-DYNAMICS STUDY OF THE VELOCITY-AUTOCORRELATION FUNCTION AND THE SELF-DIFFUSION COEFFICIENT IN MULTICOMPONENT MIXTURES

A detailed molecular-dynamics study is presented concerning the dynamic one-particle properties of binary and ternary mixtures of hard-sphere-like particles. We have studied the self-diffusion coefficient for each component of the mixture as a function of the density, and as a function of the difference in particle diameter. The results are compared with the predictions of the Enskog theory. At moderate densities positive deviations from the Enskog theory are found; at high densities we find negative deviations. It is observed that the amplitudes of these deviations differ for each component of the mixture. For moderate densities it is shown that these amplitudes have a particle-diameter dependence that is similar to that of the amplitudes of the long-time tails of the velocity-autocorrelation functions. This finding indicates that the vortex processes that give rise to the long-time tails are also responsible for the nonexponential decay of the velocity-autocorrelation function at shorter times.