Dynamic Slowdown and Spatial Correlations in Viscous Silica Melt: Perspectives from Dynamic Disorder

TL;DR

This study uses molecular dynamics simulations to explore the microscopic origins of the dynamic slowdown in amorphous silica, revealing species-dependent constraints, dynamic disorder, and growing cooperative correlations as temperature decreases.

Contribution

It provides a microscopic framework connecting dynamic disorder, species-specific constraints, and cooperative relaxation in strong glass formers, advancing understanding of the slowdown phenomenon.

Findings

Jump dynamics become slower and more intermittent at lower temperatures.

Species-dependent constraints influence relaxation, with silicon and oxygen showing different dominant neighbors.

Spatial extent of cooperative relaxation increases with cooling, linking to relaxation asymmetry.

Abstract

The dynamic slowdown in glass-forming liquids remains a central topic in condensed matter science. Here, we report a theoretical investigation of the microscopic origin of the slowdown in amorphous silica, a prototypical strong glass former with a tetrahedral network structure. Using molecular dynamics simulations, we analyze atomic jump dynamics, the elementary structural change processes underlying relaxation. We find that the jump statistics deviate from Poisson behavior with decreasing temperature, reflecting the emergence of dynamic disorder in which slowly evolving variables modulate the jump motion. The slowdown is species-dependent: for silicon, the primary constraint arises from the fourth-nearest oxygen neighbor, while at lower temperatures, the fourth-nearest silicon also becomes relevant; for oxygen, the dominant influence comes from the second-nearest silicon neighbors. As the system is cooled, the jump dynamics become increasingly slow and intermittent, proceeding in a higher-dimensional space of multiple slow variables that reflect cooperative rearrangements of the network. Species-resolved point-to-set correlations further reveal that the spatial extent of cooperative relaxation grows differently for silicon and oxygen, directly linking their relaxation asymmetry to the extent of collective motion. Together, these results provide a microscopic framework linking dynamic disorder, species-dependent constraints, and cooperative correlations, offering deeper insight into the slowdown of strong glass-forming networks.