A molecular theory of Stokes–Einstein behavior. I. Translational Brownian motion

By using the Mori generalized Langevin equation an expression for the velocity autocorrelation function of a Brownian particle is obtained. By an appropriate choice of the potential of interaction between the particle and the fluid molecules the frequency dependent friction coefficient reduces to the value found when the slip boundary condition is applied in a hydrodynamic calculation; a different choice gives almost exactly the stick value. The reasons why the previous ’’mode-coupling’’ calculations give an incorrect form for the friction coefficient are discussed.