# Atomistic structural mechanism for the glass transition: Entropic contribution

## TL;DR

This study uses atomistic simulations to reveal that the proliferation of rigid, centrosymmetric atomic structures causes the entropy kink and dynamical freezing at the glass transition, confirming the Adam-Gibbs scenario.

## Contribution

It provides an atomistic structural explanation for the glass transition, linking entropy changes to the emergence of rigid atomic structures and their role in dynamical arrest.

## Key findings

- Confirmation of the Adam-Gibbs entropy scenario.
- Identification of increased centrosymmetric structures at the transition.
- Structural proliferation explains the entropy kink and freezing-in of dynamics.

## Abstract

A popular Adam--Gibbs scenario has suggested that the excess entropy of glass and liquid over crystal dominates the dynamical arrest at the glass transition with exclusive contribution from configurational entropy over vibrational entropy. However, an intuitive structural rationale for the emergence of frozen dynamics in relation to entropy is still lacking. Here we study these issues by atomistically simulating the vibrational, configurational, as well as total entropy of a model glass former over their crystalline counterparts for the entire temperature range spanning from glass to liquid. Besides confirming the Adam--Gibbs entropy scenario, the concept of Shannon information entropy is introduced to characterize the diversity of atomic-level structures, which undergoes a striking variation across the glass transition, and explains the change found in the excess configurational entropy. Hence, the hidden structural mechanism underlying the entropic kink at the transition is revealed in terms of proliferation of certain atomic structures with a higher degree of centrosymmetry, which are more rigid and possess less nonaffine softening modes. In turn, the proliferation of these centrosymmetric (rigid) structures leads to the freezing-in of the dynamics beyond which further structural rearrangements become highly unfavourable, thus explaining the kink in the configurational entropy at the transition.