Enhanced diffusion in finite-size simulations of a fragile diatomic glass former

TL;DR

This study uses molecular dynamics to explore how finite system size affects the relaxation dynamics of a diatomic glass former, revealing unique nonmonotonic behavior and insights into cooperative motions and relaxation mechanisms.

Contribution

It demonstrates the finite-size dependence of relaxation times in a diatomic glass former, highlighting contrasting behaviors with monatomic systems and supporting defect and facilitation theories.

Findings

Relaxation time decreases with system size initially.

Cooperative motions weaken as size decreases.

Relaxation times increase again at very small sizes.

Abstract

Using molecular dynamics simulations we investigate the finite-size dependence of the dynamical properties of a diatomic supercooled liquid. The simplicity of the molecule permits us to access the microsecond time scale. We find that the relaxation time decreases simultaneously with the strength of cooperative motions when the size of the system decreases. While the decrease of the cooperative motions is in agreement with previous studies, the decrease of the relaxation time opposes what has been reported to date in monatomic glass formers and in silica. This result suggests the presence of different competing physical mechanisms in the relaxation process. For very small box sizes the relaxation times behavior reverses itself and increases strongly when the box size decreases, thus leading to a nonmonotonic behavior. This result is in qualitative agreement with defect and facilitation theories.