Seeing through the glass transition

Despite its longstanding ubiquity, fundamental aspects of glass remain mysterious. For example, researchers have struggled to establish a quantitative theory of glass transition that connects energy flow, or thermodynamics, with the dynamic movement of atoms in glass former materials, which help facilitate the formation of glass.

Parmar et al. directly linked the thermodynamics and dynamics to understand this transition. Using computer simulations, they resolved the potential energy landscape of a model glass as it cools and transitions into glass, reaching its amorphous ground state. This landscape described the energy of the model glass depending on the configuration of its atoms, which is explored over the full temperature range of the finite system.

“Our work exploits a finite system that allows essentially complete sampling of the potential energy landscape, providing a level of detail that is typically inaccessible,” said author Andreas Heuer. “This enables a particularly direct connection between thermodynamics and dynamics.”

The authors were able to quantitatively connect energy properties of the landscape with dynamical observables, such as the fragile-to-strong crossover. This is observed for glass formers such as silica and water when they’re cooled to lower temperatures but is not seen experimentally for fragile glass formers. This has been challenging to interpret from a thermodynamic point of view, but the landscape provides a way: The authors found that the fragile-to-strong crossover arises at temperatures when the number of accessible low-energy states starts to be depleted compared to a standard Gaussian distribution.

“The framework can be extended to other model systems to test how general the thermodynamics — [1][2]dynamics link is and how it depends on interaction details or dimensionality,” Heuer said.

Next, the authors will explore the depletion of low-energy states in experimentally relevant glass-forming materials, such as silica.

Source: “Starting from the amorphous ground state: linking landscape thermodynamics to slow dynamics and crossover,” by Anshul D. S. Parmar, Simon G. Kellers, and Andreas Heuer, Journal of Chemical Physics (2026). The article can be accessed at https://doi.org/10.1063/5.0325432 .