Crossover in dynamics in the Kob-Andersen binary mixture glass-forming liquid

TL;DR

This study computationally investigates the Kob-Andersen glass-forming liquid, revealing a dynamical crossover around the mode coupling temperature, with implications for understanding fragile to strong transitions in glassy materials.

Contribution

It provides evidence of a dynamical crossover in the Kob-Andersen model below the mode coupling temperature, linking it to fragile to strong behavior in glass formers.

Findings

Relaxation times show a crossover near T_MCT.

Dynamical heterogeneity mirrors the crossover.

Adam-Gibbs relation remains valid below T_MCT with corrections.

Abstract

Glass-forming liquids are broadly classified as being fragile or strong, depending on the deviation from Arrhenius behavior of their relaxation times. A fragile to strong crossover is observed or inferred in liquids like water and silica, and more recently also in metallic glasses and phase change alloys, leading to the expectation that such a crossover is more widely realised among glass formers. We investigate computationally the well-studied Kob-Andersen model, accessing temperatures well below the mode coupling temperature $T_{MCT}$. We find that relaxation times exhibit a crossover in dynamics around $T_{MCT}$, and discuss whether it bears characteristics of the fragile to strong crossover. Several aspects of dynamical heterogeneity exhibit behavior mirroring the dynamical crossover, whereas thermodynamic quantities do not. In particular, the Adam-Gibbs relation describing the relation between relaxation times and configurational entropy continues to hold below the dynamical crossover, when anharmonic corrections to the vibrational entropy are included.