Dynamical correlations in a binary metastable fluid

Abstract

Results from a molecular dynamics study of isobarically, supercooled binary fluids of Lennard-Jones particles are presented to show that systematic changes in the behavior of the density, diffusion and shear viscosity coefficients, and density correlation functions point to a broad transition signifying an underlying change in the nature of the particle dynamics, from fluid-like motions to jumps over potential energy minima. This conclusion provides support of a previous study of single-component Lennard-Jones fluids under isothermal compression along with its implications concerning the validity of recent mode-coupling theories. Also presented here are two related results. First, a comparison of density correlation functions between the supercooled states and equilibrium crystalline states at the same temperatures and pressure demonstrates explicitly the existence of long relaxation times in the decay of density fluctuations in a system that is out of equilibrium. Second, a series of mean square displacement results, based on long simulation runs, shows the onset of large variations due to changes in the local atomic environments. This behavior is associated with a characteristic negative curvature in the growth of the mean square displacement