Accuracy of Enskog theory for rotational versus translational motion: A molecular-dynamics study

Abstract

Molecular-dynamics simulations of fluids composed of hard ellipsoids yield translational diffusional coefficients that deviate from the predictions of kinetic theory in the same way, but to a greater degree than, those of hard spheres. Surprisingly, however, the rotational diffusion coefficients are closely predicted by Enskog theory for all but the highest densities. However, for both motions, even at zero density, there are small deviations from kinetic theory, presumably due to chattering recollisions. Though the phase diagram is approximately symmetric between prolate and oblate ellipsoids of the same asymmetry, the dynamical properties are not. No existing theory explains these observations.