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

For a very dense binary liquid of hard spheres the dependence of the veloci ty-autocorrelation function (VAF) of tagged particles and of the self-diffu sion coefficient on system size is derived from the coupling of self diffus ion to modes of collective flow. Collective flow is described by longitudin al and transverse current-current correlation functions for different wavev ectors which are obtained by molecular dynamics simulation. The size depend ence of the VAF is reproduced rather accurately for longer times t > 7 tau, where tau is the mean time of free flight. The result for the size depende nce of the self-diffusion coefficient is in satisfactory agreement with a d irect calculation, but this result also depends on the VAF's at shorter tim es.