Diffusional Anomaly and network dynamics in liquid silica

TL;DR

This study uses power spectral analysis of molecular dynamics simulations to link diffusional anomalies in liquid silica with network dynamics and multiple time-scale behavior, revealing how structural changes influence diffusivity.

Contribution

It introduces a novel application of power spectral analysis to liquid silica, demonstrating the connection between vibrational mode coupling, network reorganization, and diffusional anomalies.

Findings

Power spectrum of silica shows 1/f dependence indicating multiple time-scale behavior.

Diffusional anomalies correlate with changes in local tetrahedral order and vibrational coupling.

Structural and diffusional anomalies are linked through symmetry-dependent vibrational interactions.

Abstract

The present study applies the power spectral analysis technique to understand the diffusional anomaly in liquid silica, modeled using the BKS potential. Molecular dynamics simulations have been carried out to show that power spectrum of tagged particle potential energy of silica shows a regime with 1/f dependence on frequency f which is the characteristic signature of multiple time-scale behaviour in networks. As demonstrated earlier in the case of water (J. Chem. Phys., 122, 104507 (2005)), the variations in the mobility associated with the diffusional anomaly are mirrored in the scaling exponent alpha associated with this multiple time-scale behaviour. Our results indicate that in the anomalous regime, as the local tetrahedral order decreases with temperature or pressure, the coupling of local modes to network reorganisations increases and so does the diffusivity. This symmetry-dependence of the vibrational couplings is responsible for the connection between the structural and diffusional anomalies.