Tuning Pairwise Potential Can Control the Fragility of Glass-Forming Liquids: From Tetrahedral Network to Isotropic Soft Sphere Models

TL;DR

This study uses molecular dynamics simulations to show how tuning the pairwise potential in a glass-forming model can control its fragility, revealing links between structure, dynamics, and thermodynamics across different glass formers.

Contribution

It demonstrates that adjusting the pairwise potential depth in a single model system can systematically control fragility, bridging network and isotropic glass formers and providing mechanistic insights.

Findings

Fragility can be tuned from strong to fragile by changing potential depth.

The crossover from Arrhenius to super-Arrhenius behavior is observed.

Fragility correlates with thermodynamic anomalies such as specific heat peaks.

Abstract

We perform molecular dynamics simulations for a silica glass former model proposed by Coslovich and Pastore (CP) over a wide range of densities. The density variation can be mapped onto the change of the potential depth between Si and O interactions of the CP model. By reducing the potential depth (or increasing the density), the anisotropic tetrahedral network structure observed in the original CP model transforms into the isotropic structure with the purely repulsive soft-sphere potential. Correspondingly, the temperature dependence of the relaxation time exhibits the crossover from the Arrhenius to the super-Arrhenius behavior. Being able to control the fragility over a wide range by tuning the potential of a single model system helps us to bridge the gap between the network and isotropic glass formers and to obtain the insight into the underlying mechanism of the fragility. We study the relationship between the fragility and dynamical properties such as the magnitude of the Stokes-Einstein violation and the stretch exponent in the density correlation function. We also demonstrate that the peak of the specific heat systematically shifts as the density increases, hinting that the fragility is correlated with the hidden thermodynamic anomalies of the system.