The velocity autocorrelation function and self-diffusion coefficient of fluids with steeply repulsive potentials

Author： Heyes David M. Powles Jack G. Rickayzen Gerald

ISSN： 1362-3028

Source： Molecular Physics, Vol.100, Iss.5, 2002-03, pp. : 595-610

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Abstract

We consider the velocity autocorrelation function, vacf, or C_v(t) and self-diffusion coefficients, D, of steeply repulsive inverse power fluids (SRP) in which the particles interact with a pair potential, &phis;(r) = ε(σ/r)n. The C_v(t) are calculated numerically by molecular dynamics simulations. Accurate expressions for the short time expansion of C_v(t) to order O (t⁴) for n large are derived for this fluid. We propose novel expressions for C_v(t) that, for n large, spans the transition from the short time regime (expandable in even powers of time) and the longer time exponential-like regime characteristic of hard spheres. Inter alia we introduce relaxation times that characterize the duration of a collision and the decay of the velocity correlation within the mean-collision or Enskog-like relaxation time, τ_E.