A scaled Boltzmann theory for k-dependent test particle correlation functions in moderately dense gasesa)

Abstract

Applicability of the hard sphere Boltzmann-Lorentz-Enskog test particle kinetic equation to the study of self-diffusion in moderately dense gases is assessed by comparing the numerical solutions of the equation for the velocity autocorrelation function, the kinetic energy autocorrelation function and the k -dependent test particle position correlation function with data generated from computer molecular dynamics and also with an incoherent quasielastic neutron scattering experiment. In order to adapt the hard sphere theory to explain data generated from systems in which particles interact via continuous potentials, the following procedure has been tested: We fix the effective collision frequency in the hard sphere kinetic equation by using the experimentally measured value of the self-diffusion coefficient. The results of the comparison show that this "scaled Boltzmann theory" compares well with the data for a system with a purely repulsive potential up to fairly high densities; however, increasing deviations are noticeable for a system in which the attractive part of the potential is included. This is so, especially at lower temperatures.3730