A non-equilibrium molecular dynamics method for the calculation of the mutual diffusion coefficient for a mixture of hard spheres was described. The method was applied to a 50-50 mixture of equi-diameter particles having a mass ratio of 0.1 for the two species, at a volume of three times close-packing. By extrapolating the results to the limit of vanishing concentration gradient and infinite system size, a value was obtained which was in statistical agreement with the result obtained using a Green-Kubo molecular dynamics procedure, which was also described. The non-equilibrium calculation yields a mutual diffusion coefficient which decreased slightly with increasing concentration gradient. The Green-Kubo time correlation function for mutual diffusion displayed a slow decay with time, qualitatively similar to the long-time tail which was predicted by the hydrodynamic theory of Pomeau.

Calculation of the Mutual Diffusion Coefficient by Equilibrium and Non-Equilibrium Molecular Dynamics. Erpenbeck, J.J., Kincaid, J.M.: International Journal of Thermophysics, 1986, 7[2], 305-17