Comment on "Kinetic theory of single-particle motion in a fluid"

Abstract

The reason Mehaffey and Cukier did not obtain the hydrodynamic Stokes-Einstein relation for the diffusion coefficient of a large particle from kinetic theory is that they did not carry their calculation far enough. When the terms in the repeated-ring sum are evaluated more completely and then summed, the proper hydrodynamic Stokes-Einstein form is obtained. This procedure does not affect Mehaffey and Cukier's results for the long time behavior of the velocity-autocorrelation function. Some inconsistent approximations in Mehaffey and Cukier's ring sum are also discussed here.