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Updated: Jun 18, 2026

Analyzing Melts and Fluids from Ab Initio Molecular Dynamics Simulations with the UMD Package
Published on: September 17, 2021
Computing the viscosity of supercooled liquids. II. Silica and strong-fragile crossover behavior
Akihiro Kushima1, Xi Lin, Ju Li
1Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. kushima@mit.edu
Abstract:
A recently developed atomistic method capable of calculating the fragile (non-Arrhenius) temperature behavior of highly viscous liquids is further tested by studying a model of SiO(2), a glass former well known for its Arrhenius temperature behavior (strong). The method predicts an Arrhenius temperature variation, in agreement with experiments, the origin of which is revealed by both quantitative and qualitative results on transition state pathways, activation barrier analysis, energy landscape connectivity, and atomistic activation mechanisms. Also predicted is a transition from fragile to strong behavior at a lower viscosity, below the range of measurements, which had been previously suggested on the basis of molecular dynamics simulations. By systematically comparing our findings with corresponding results on the binary Lennard-Jones system (fragile) we gain new insights into the topographical features of the potential energy landscape, characteristics that distinguish strong from fragile glassy systems. We interpret fragility as a universal manifestation of slowing of dynamics when the system becomes trapped in deep energy basins. As a consequence, all glass-forming systems, when cooled from their normal liquid state, should exhibit two transitions in temperature scaling of the viscosity, a strong-to-fragile crossover followed by a second transition reverting back to strong behavior.
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