Spatial Correlations of Mobility and Immobility in a Glassforming Lennard-Jones Liquid

TL;DR

This study uses molecular dynamics simulations to analyze spatial correlations in particle mobility within a glass-forming Lennard-Jones liquid, revealing temperature-dependent clustering behaviors linked to energy and composition fluctuations.

Contribution

It provides detailed characterization of local atomic motions and identifies growing spatial correlations and cluster sizes as temperature decreases, especially near the mode-coupling transition.

Findings

Immobile particles form compact clusters

Mobile particles form string-like clusters

Correlation length diverges near mode-coupling temperature

Abstract

Using extensive molecular dynamics simulations of an equilibrium, glass-forming Lennard-Jones mixture, we characterize in detail the local atomic motions. We show that spatial correlations exist among particles undergoing extremely large (``mobile'') or extremely small (``immobile'') displacements over a suitably chosen time interval. The immobile particles form the cores of relatively compact clusters, while the mobile particles move cooperatively and form quasi-one-dimensional, string-like clusters. The strength and length scale of the correlations between mobile particles are found to grow strongly with decreasing temperature, and the mean cluster size appears to diverge at the mode-coupling critical temperature. We show that these correlations in the particle displacements are related to equilibrium fluctuations in the local potential energy and local composition.