Free Volume cannot Explain the Spatial Heterogeneity of Debye-Waller factors in a Glass-Forming Binary Alloy

TL;DR

This study shows that free volume does not account for the spatial heterogeneity of Debye-Waller factors in a glass-forming alloy, challenging previous assumptions about their relationship.

Contribution

The paper demonstrates through simulations that free volume is not correlated with local Debye-Waller factors, highlighting a different origin of dynamic heterogeneity in glasses.

Findings

Free volume shows no significant spatial correlation with Debye-Waller factors.

Debye-Waller heterogeneity occurs over short trajectories, independent of free volume.

Spatial variation in free volume does not cause dynamic heterogeneity.

Abstract

We examine the relation between the free volume per particle and the variance of the particle position, equivalent to a local Debye-Waller (DW) factor for a 2D glass-forming alloy using molecular dynamics simulations. We find that the latter quantity exhibits significant spatial heterogeneity despite involving trajectories two orders of magnitude shorter than those typically used to measure such heterogeneities. We find that the free volume exhibits no significant spatial correlation with the local DW factor. We conclude that the spatial variation in local free volume is not the cause of the short time dynamic heterogeneity.