Molecular-dynamics study of glassy and supercooled states of a binary mixture of soft spheres.

Abstract

A series of molecular-dynamics simulations of binary-fluid mixtures composed of softly repelling spheres have been made as part of an investigation of the glass-forming properties of mixtures. These mixtures are simple prototypes of glass-forming systems, as both randomness and frustration are intrinsic to them. The randomness is inherent in the fluid and frustration is due to the large, local rearrangement of atoms required for the formation of a crystal from a fluid or glassy configuration. The equation of state, pair and triplet correlation functions, single-particle velocity time autocorrelation functions, and some measures of local glassy order have been determined for a range of compositions, X, and effective reduced densities, ${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{eff}}$=(${\mathrm{n}}^{\mathrm{*}}$/${\mathrm{T}}^{\mathrm{*}1/4}$)(${\mathrm{\ensuremath{\sigma}}}_{\mathrm{eff}}$/${\mathrm{\ensuremath{\sigma}}}_{11}$${)}^{3}$ where ${\ensuremath{\sigma}}_{\mathrm{eff}}$ is the one-fluid van der Waals equivalent diameter. In addition, attention has been focused on the relaxation of some anisotropic correlation functions characterizing the local environment. Attempts have been made to analyze some of these quantities using plausible phenomenological models. The changes in these quantities which occur as the fluid is supercooled and finally forms a glass are examined and the possible implication of these findings for certain dynamical theories of the glass transition are discussed. Calculations have also been performed to determine compositional conditions necessary for a supercooled liquid to crystallize and the relevance of this to recent experiments is discussed.