title: Novel computational probes of diffusive motion.
abstract: Self-diffusion constants, D, and the atomic-level processes that produce them have been investigated numerically for the binary-mixture Lennard-Jones (BMLJ) model and for liquid silica as described by the Van Beest-Kramer-Van Santen interaction model. The primary conceptual tool for this study is the joint probability distribution for single particles as a function of initial velocity and positional displacement at a given later instant. Self-diffusion constants can be expressed exactly in terms of this probability function. The numerical simulations for the BMLJ case reveal an unusual temperature effect; in contrast to the high-temperature behavior, particles with high initial velocities experience disproportionate retardation in forward displacement. In the silica modeling simulations, diffusive processes have been compared at constant-temperature "isodiffusive" pairs of states, demonstrating a significant role played by the amount of local tetrahedral order that is present in the medium.
authors.affiliation: Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: M Scott
authors.initials: MS
authors.lastname: Shell
authors.forename: Pablo G
authors.initials: PG
authors.lastname: Debenedetti
authors.forename: Frank H
authors.initials: FH
authors.lastname: Stillinger