Molecular dynamics study of the longitudinal modes in disparate-mass binary liquid mixtures - art. no. 021202

A series of molecular dynamics simulations of simple liquid binary mixtures of soft spheres with disparate-mass particles were carried out to investig ate the origin of the marked differences between the dynamic structure fact ors of some liquid binary mixtures such as the Li0.7Mg0.3 and Li0.8Pb0.2 al loys. It is shown that the facility for observing peaks associated with fas t-propagating modes in the partial Li-Li dynamic structure factor of Li0.8P b0.2 should be mainly attributed to the structure of this alloy, which is c haracterized by an incipient ABAB ordering as found in molten salts. The lo ngitudinal dispersion relations at intermediate wave vectors obtained from the longitudinal current spectra are very similar for the two alloys and re flect the existence of both fast-and slow-propagating modes of kinetic char acter associated with light and heavy particles, respectively. The influenc e of the hardness of the repulsive potential cores as well as the compositi on of the mixture on the longitudinal collective modes is also discussed.