Short-wavelength collective density excitations in monatomic liquids

Abstract

Computer simulation data for liquids with generalized Lennard-Jones potentials are analysed with the aim of elucidating the key features required of a liquid for it to support a short-wavelength, collective density excitation. The data suggest that, for high densities, both the repulsive and attractive components of the Lennard-Jones potential must be modified substantially for such a mode to exist, and that softening the potential core does not in itself suffice to induce the correlation necessary for a liquid to support a mode. Viscoelastic theory is shown to provide a good description of the dynamical properties and to provide a useful condition for the existence of a collective density excitation.