Dynamic propensity in a kinetically constrained lattice gas

TL;DR

This paper investigates dynamic heterogeneity in a kinetically constrained lattice gas model, showing that local propensity correlates with extended particle clusters rather than simple structural features, revealing fundamental excitations.

Contribution

It introduces the use of dynamic propensity in the (2)-TLG model and identifies extended clusters as key excitations linked to dynamical heterogeneity.

Findings

Propensity field effectively measures dynamical heterogeneity.

Extended particle clusters correlate with propensity.

Propensity is not linked to simple structural properties.

Abstract

We apply the concept of dynamic propensity to a simple kinetically constrained model of glass formers, the two-vacancy assisted triangular lattice gas, or (2)-TLG. We find that the propensity field, defined in our case as the local root-mean square displacement averaged over the ensemble of trajectories with identical initial configurations, is a good measure of dynamical heterogeneity. This suggests a configurational origin for spatial fluctuations of the dynamics, but just as in the case of atomistic systems, we find that propensity is not correlated to any simple structural property. We show instead that certain extended clusters of particles connected to vacancies correlate well with propensity, indicating that these are the fundamental excitations of the (2)-TLG. We also discuss time-correlations and the correlation between configurations within the propensity ensemble.