Dynamics and energy landscape in a tetrahedral network glass-former: Direct comparison with models of fragile liquids

TL;DR

This study uses molecular dynamics simulations to analyze a simple tetrahedral network glass-former model, revealing how its energy landscape and unstable modes influence its dynamic heterogeneity compared to fragile liquids.

Contribution

It introduces a new spherical potential model for tetrahedral network glass-formers and compares its properties with fragile liquids, linking energy landscape features to dynamics.

Findings

Network glass-former shows fewer extended unstable modes.

Localized unstable modes relate to bond rearrangements.

Fragile liquids exhibit more cooperative unstable modes.

Abstract

We report Molecular Dynamics simulations for a new model of tetrahedral network glass-former, based on short-range, spherical potentials. Despite the simplicity of the forcefield employed, our model reproduces some essential physical properties of silica, an archetypal network-forming material. Structural and dynamical properties, including dynamic heterogeneities and the nature of local rearrangements, are investigated in detail and a direct comparison with models of close-packed, fragile glass-formers is performed. The outcome of this comparison is rationalized in terms of the properties of the Potential Energy Surface, focusing on the unstable modes of the stationary points. Our results indicate that the weak degree of dynamic heterogeneity observed in network glass-formers may be attributed to an excess of localized unstable modes, associated to elementary dynamical events such as bond breaking and reformation. On the contrary, the more fragile Lennard-Jones mixtures are characterized by a larger fraction of extended unstable modes, which lead to a more cooperative and heterogeneous dynamics.