Fokker-Planck dynamics of interacting Brownian particles

Starting from an N-particle Fokker-Planck equation, the results for the concentration autocorrelation function are presented. It is shown that the corresponding memory function has the physical meaning of a (k- omega )-dependent longitudinal viscosity. A numerical mode-mode coupling calculation of the wavevector dependence of the longitudinal viscosity is found to be in good agreement with experimental results. Comparing the Fokker-Planck results with the corresponding Smoluchowski results show that the latter are only valid for small wavevectors or small interaction strength.