# How do packing defects modify the cooperative motions in supercooled liquids ?

## TL;DR

This study uses molecular dynamics simulations to explore how packing defects, introduced by probes of different sizes, influence the cooperative motions and dynamic heterogeneity in supercooled liquids, revealing size-dependent effects on dynamics.

## Contribution

It demonstrates how local packing modifications by probes of different sizes significantly alter the dynamics and heterogeneity in supercooled liquids, providing insight into defect-driven dynamic behavior.

## Key findings

- Small probes accelerate dynamics and reduce heterogeneity.
- Large probes slow down dynamics and increase heterogeneity.
- Effects diminish near the onset temperature of cage dynamics.

## Abstract

We use molecular dynamic simulations to investigate the relation between the presence of packing defects in a glass-former and the spontaneous cooperative motions called dynamic heterogeneity. For that purpose we use a simple diatomic glass-former and add a small number of larger or smaller diatomic probes. The diluted probes modify locally the packing, inducing structural defects in the liquid, while we find that the number of defects is small enough not to disturb the average structure. We find that a small packing modification around a few molecules can deeply influence the dynamics of the whole liquid, when supercooled. When we use small probe molecules, the dynamics accelerates and the dynamic heterogeneity decreases. In contrast, for large probes the dynamics slows down and the dynamic heterogeneity increases. The induced heterogeneities and transport coefficient modification increase when the temperature decreases and disappear around the onset temperature of the cage dynamics.