Constrained dynamics of localized excitations causes a non-equilibrium phase transition in an atomistic model of glass formers

TL;DR

This study uses molecular dynamics and importance sampling to investigate non-equilibrium phase transitions in glass formers, revealing exponential tails and inactive phases linked to dynamic constraints.

Contribution

It provides empirical evidence for phase transitions in trajectory space of glass formers, connecting dynamic facilitation theory with atomistic simulations.

Findings

Exponential tails appear in long-time displacement distributions.

Reweighting trajectories reveals a phase transition into an inactive phase.

Structural differences between phases are minimal.

Abstract

Dynamic facilitation theory assumes short-ranged dynamic constraints to be the essential feature of supercooled liquids and draws much of its conclusions from the study of kinetically constrained models. While deceptively simple, these models predict the existence of trajectories that maintain a high overlap with their initial state over many structural relaxation times. We use molecular dynamics simulations combined with importance sampling in trajectory space to test this prediction through counting long-lived particle displacements. For observation times longer than the structural relaxation time exponential tails emerge in the probability distribution of this number. Reweighting trajectories towards low mobility corresponds to a phase transition into an inactive phase. While dynamics in these two phases is drastically different structural measures show only slight differences. We discuss the choice of dynamic order parameter and give a possible explanation for the microscopic origin of the effective dynamic constraints.