Distribution of atomic rearrangement vectors in a metallic glass

TL;DR

This study uses molecular dynamics simulations to analyze atomic rearrangements in metallic glasses, revealing a power-law distribution of cage-breaking probabilities and insights into the accessible rearrangement vectors related to activation barriers.

Contribution

It provides detailed statistical analysis of atomic rearrangements and their activation barriers in metallic glasses, highlighting the relationship between energy barriers and rearrangement pathways.

Findings

Majority of atoms are strongly caged with few high-propensity rearrangements.

Atoms with lower activation barriers explore fewer rearrangement vectors.

Rearrangement probability follows a power-law distribution.

Abstract

Short-timescale atomic rearrangements are fundamental to the kinetics of glasses and frequently dominated by one atom moving significantly (a rearrangement), while others relax only modestly. The rates and directions of such rearrangements (or hops) are dominated by the distributions of activation barriers (Eact) for rearrangement for a single atom and how those distributions vary across the atoms in the system. We have used molecular dynamics simulations of Cu50Zr50 metallic glass below Tg in an isoconfigurational ensemble to catalog the ensemble of rearrangements from thousands of sites. The majority of atoms are strongly caged by their neighbors, but a tiny fraction has a very high propensity for rearrangement, which leads to a power-law variation in the cage-breaking probability for the atoms in the model. In addition, atoms generally have multiple accessible rearrangement vectors, each with its own Eact. However, atoms with lower Eact (or higher rearrangement rates) generally explored fewer possible rearrangement vectors, as the low Eact path is explored far more than others. We discuss how our results influence future modeling efforts to predict the rearrangement vector of a hopping atom.