Composition and concentration anomalies for structure and dynamics of Gaussian-core mixtures

TL;DR

This study uses molecular dynamics simulations to explore how Gaussian-core mixtures exhibit anomalous diffusion and structural behaviors at different concentrations and compositions, revealing decoupled dynamics and a scaling law linking diffusivity to entropy.

Contribution

It uncovers concentration- and composition-dependent anomalies in structure and dynamics of Gaussian-core mixtures, introducing a scaling law connecting diffusivity and excess entropy.

Findings

Larger particles can become more mobile than smaller ones at high concentrations.

Tracer diffusivities show non-monotonic dependence on concentration and composition.

Structural correlations correlate with dynamic anomalies via a scaling law.

Abstract

We report molecular dynamics simulation results for two-component fluid mixtures of Gaussian-core particles, focusing on how tracer diffusivities and static pair correlations depend on temperature, particle concentration, and composition. At low particle concentrations, these systems behave like simple atomic mixtures. However, for intermediate concentrations, the single-particle dynamics of the two species largely decouple, giving rise to the following anomalous trends. Increasing either the concentration of the fluid (at fixed composition) or the mole fraction of the larger particles (at fixed particle concentration) enhances the tracer diffusivity of the larger particles, but decreases that of the smaller particles. In fact, at sufficiently high particle concentrations, the larger particles exhibit higher mobility than the smaller particles. Each of these dynamic behaviors is accompanied by a corresponding structural trend that characterizes how either concentration or composition affects the strength of the static pair correlations. Specifically, the dynamic trends observed here are consistent with a single empirical scaling law that relates an appropriately normalized tracer diffusivity to its pair-correlation contribution to the excess entropy.