Identifying the relevant parameters in design strategies for stable glasses

TL;DR

This paper investigates the parameters influencing glass stability, challenging the idea that physical quantities like particle diameter dynamics are causally responsible, and emphasizes the importance of dynamical processes.

Contribution

It introduces computational methods to optimize physical properties without altering particle diameters and demonstrates that these do not lead to enhanced glass stability.

Findings

Optimizing physical quantities alone does not produce more stable glasses.

Physical quantities are correlated but not causally responsible for ultrastability.

Dynamical processes, not static physical quantities, govern glass stability.

Abstract

A glass is conventionally obtained by cooling a bulk supercooled liquid through its glass transition temperature. The discovery of ultrastable glasses prepared using physical vapor deposition, together with the recent multiplication of numerical algorithms created to increase the stability of glasses, demonstrates the existence of a variety of strategies for designing glasses with different physical properties. This raises a broader question: which parameters most strongly govern the enhancement of glass stability? Existing computational strategies often produce highly stable glasses by optimizing certain physical properties through dynamical changes in particle diameters. We challenge the idea that these physical quantities are causally responsible for glass stability and suggest instead that diameter dynamics is the principal source of enhanced stability. To support our view, we introduce computational methods to optimize physical quantities without changing the particle diameters. Using the examples of enhanced hyperuniformity at large scale and local ordering at small scale, we design glass configurations with highly optimized values compared to bulk equilibrium states. However, these glasses do not show enhanced stability. The proposed physical quantities are correlated with glass stability, but are not causally responsible for ultrastability. These findings indicate that design rules for stable glasses should be reinterpreted in terms of the dynamical processes that generate stability, rather than the optimized physical quantities they target.