Collective excitations in classical liquids

Abstract

A simple modification of the theory of Hubbard and Beeby (1969) for collective motions in classical liquids is proposed. The modified version is based on a generalized mean-field approximation. The mean field is determined using the zeroth-moment relation. The modified version of the theory now exactly satisfies the zeroth, second and fourth frequency moments of the dynamical structure factor. Numerical calculations have been carried out for the spectral function of the longitudinal current correlations for liquid argon in the range of momentum transfer 0.5-6.3 AA⁻¹. A remarkable improvement over the results obtained from the theory of Hubbard and Beeby has been achieved and the results are in overall good agreement with the molecular-dynamics calculations.