Damping of collective modes in liquid metals. II

Abstract

For pt.I see ibid., vol.8, p.89 (1975). Calculations are reported of the memory function associated with the longitudinal current correlations along with some results for the density fluctuation spectrum for a model of liquid rubidium. The latter are compared with the information about the dynamics of density fluctuations obtained from molecular dynamics computations and neutron scattering experiments on the liquid near its melting point. The fourth frequency moment has played an essential role in generalized hydrodynamic or viscoelastic theories of the dynamic structure factor. However, the fourth moment is infinite for the rigid core potential and yet the rigid sphere fluid is frequently used as a model for real liquids. It is argued that a theory of the density fluctuation spectrum of a liquid should accurately describe the short-range collision processes, so that the rigid core limit can be recovered, even if this can only be achieved, as with the present approach, at the expense of the fourth moment condition.