Velocity Autocorrelations for Hard Spheres

Abstract

A study of the velocity autocorrelation function for hard spheres over the entire fluid density region shows that deviations from exponential behavior are small. At very low density a small positive deviation is found which is accounted for in the Boltzmann theory of the self-diffusion coefficient. At higher densities the principal non-Markovian process is identified with a surprisingly long persistence of velocity currents. At still higher densities, near solidification, anticorrelating backscattering events predominate.