A new way to explore and navigate low energy states of glasses

What is it about?

Many materials solidify and drop out of equilibrium when cooled below their glass transition temperature. This difficulty of glasses with finding their lowest-energy configurations is often attributed to their potential energy landscapes: rugged, barrier-filled surfaces spanning an abstract high-dimensional configuration space. Computational approaches typically also find that these surfaces are very difficult to navigate. We report that for three glassy systems the energy landscapes are unexpectedly pervaded by narrow and deep canyon-like structures, with glassy states and the earlier-noted rugged surfaces lining the canyon floors. Our computational approach, based on a method called metadynamics, shows that the canyons’ walls can be used for effective navigation, and be followed directly to progressively lower energy states.

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Photo by Joe Gardner on Unsplash

Photo by Joe Gardner on Unsplash

Why is it important?

Our study gives several insights into the nature of glassy states and the glass transition. For one, the canyons are very narrow, and become narrower as they meander to lower energy. The resulting entropic penalty may effectively prevent a glass (or a conventional simulation of a glass) from ever reaching the lowest energy states. Moreover, when we studied the shape of the canyon floors, they were found to be low-dimensional and roughly fractal; remarkably, the shapes of the canyon floors in the landscapes in three different glass models were very similar. This might provide an explanation for how different glasses can display such similar phenomena when cooled. Lastly, the discovery of these canyons should inspire new methods for discovering very low energy glassy states, providing insights into glasses and perhaps related problems such as protein folding or deep learning.

Perspectives