Density-temperature-softness scaling of the dynamics of glass-forming soft-sphere liquids

We employ the principle of dynamic equivalence between soft-sphere and hard-sphere fluids to describe the interplay of the effects of varying the density n, the temperature T, and the softness (characterized by a softness parameter ν^-1) on the dynamics of glass-forming soft-sphere liquids in terms of simple scaling rules. The main prediction is the existence of a dynamic universality class associated with the hard-sphere fluid, constituted by the soft-sphere systems whose dynamic parameters depend on n, T, and ν only through the reduced density n^*nσ _HS(T^*,ν). A number of scaling properties observed in recent experiments and simulations involving glass-forming fluids with repulsive short-range interactions are found to be a direct manifestation of this general dynamic equivalence principle.