Dynamics in a tetrahedral network glassformer: vibrations, network rearrangements, and diffusion

Area of Science:

• Condensed matter physics
• Materials science
• Computational chemistry

Background:

• Tetrahedral network glassformers like SiO2 exhibit complex dynamics.
• Understanding particle vibrations and network rearrangements is crucial for predicting material properties.

Purpose of the Study:

• To investigate the anisotropic vibrations and dynamic heterogeneity in a viscous SiO2 model.
• To explore the relationship between network structure, particle motion, and the Stokes-Einstein relation.

Main Methods:

• Molecular dynamics simulations using a Coslovich and Pastore model for SiO2.
• Analysis of time-averaged vibration tensors represented by ellipsoids.
• Calculation of diffusion constants and viscosity.

Main Results:

• Observed marked vibrational heterogeneity and anisotropic vibrations correlated with the network structure.
• Identified diffusion via particle jumps and network reorganization.
• Found weak violation of the Stokes-Einstein relation due to T-dependent contributions from surrounding particles.

Conclusions:

• Silica exhibits mild crossover in Stokes-Einstein relation due to low coordination numbers.
• Dynamic heterogeneity arises from localized jump events on long timescales.
• Diffusion follows activation dynamics, analyzable via irreversible jump analysis.