Size dependence of self-diffusion in dense binary liquid of hard spheres

Abstract
For a very dense binary liquid of hard spheres the dependence of the velocity-autocorrelation function (VAF) of tagged particles and of the self-diffusion coefficient on system size is derived from the coupling of self diffusion to modes of collective flow. Collective flow is described by longitudinal and transverse current-current correlation functions for different wavevectors which are obtained by molecular dynamics simulation. The size dependence of the VAF is reproduced rather accurately for longer times t > 7τ, where τ is the mean time of free flight. The result for the size dependence of the self-diffusion coefficient is in satisfactory agreement with a direct calculation, but this result also depends on the VAF's at shorter times.