Studies in molecular dynamics. XIV. Mass and size dependence of the binary diffusion coefficient

The velocity autocorrelation function and the binary diffusion coefficient of a single hard sphere test particle whose mass and size is less than that of the solvent are computed in the dense fluid phase. Large deviations from the Enskog theory of uncorrelated motion are found as the diffusion coefficient vanishes for the lighter and larger test particle at higher densities. Comparison with experimental values leads to the conclusion that the correlated motions observed in hard spheres correspond well to those observed in real systems.