Structural signatures of strings and propensity for mobility in a simulated supercooled liquid above the glass transition

TL;DR

This study uses molecular dynamics simulations to explore the structural environments associated with string-like particle motion in a supercooled liquid, revealing a link between local structure, mobility, and the onset of glassy dynamics.

Contribution

It identifies the structural signatures of mobile particles in strings and establishes their relation to the emergence of icosahedral order and non-Arrhenius behavior.

Findings

String-like motion occurs at boundaries between ordered and disordered regions.

The onset of string motion coincides with the appearance of icosahedral clusters.

A structural criterion predicts particles with higher mobility propensity.

Abstract

By molecular dynamics (MD) simulation of the one-component Dzugutov liquid in a metastable equilibrium supercooled state approaching the glass transition, we investigate the structural properties of highly mobile particles moving in strings at low temperature T where string-like particle motion (SLM) is well developed. We find that SLM occurs most frequently in the boundary regions between clusters of icosahedrally-ordered particles and disordered, liquid-like, domains. Further, we find that the onset T for significant SLM coincides with the T at which clusters of icosahedrally-ordered particles begin to appear in considerable amounts, which in turn coincides with the onset T for non-Arrhenius dynamics. We find a unique structural environment for strings that is different from the structure of the bulk liquid at any T. This unique string environment persists from the melting T upon cooling to the lowest T studied in the vicinity of the mode-coupling temperature, and is explained by the existence of rigid elongated cages. We also form a criterion based solely on structural features of the local environment that allow the identification of particles with an increased propensity for mobility.