Dynamical correlations in dense metastable fluids

Molecular-dynamics simulation results on soft-sphere fluids are presented that show the systematic changes in the equation of state, pair distribution function, self-diffusion coefficient, and various time-correlation functions with density at constant temperature in the metastable density region beyond the normal liquid range. At a characteristic density in this region, a decrease in the compressibility is observed along with a change in the density variation of the self-diffusion coefficient and the onset of a slowly decaying component in the density-correlation function. We interpret these behaviors as manifestations of a transition in which the particle dynamics changes its basic character, from collisions among particles undergoing continuous fluidlike displacements to barrier hopping of individual particles trapped in local-potential-energy minima. It is also concluded that this transition is distinct from the glass transition that occurs at a higher density.