The Origin of the Decoupling of Oxygen and Silicon Dynamics in Liquid Silica as Expressed by its Potential Energy Landscape

TL;DR

This study investigates the decoupling of oxygen and silicon dynamics in liquid silica using computer simulations and potential energy landscape analysis, revealing that rotational processes cause oxygen mobility to differ from silicon.

Contribution

It provides a detailed explanation of the origin of oxygen-silicon decoupling in silica based on potential energy landscape analysis and identifies rotational processes as the key factor.

Findings

Decoupling of oxygen and silicon dynamics observed upon cooling.

Rotational processes are responsible for oxygen mobility differences.

Insights into silica's potential energy landscape and relaxation processes.

Abstract

The oxygen and silicon dynamics in silica is compared via computer simulations. In agreement with experimental data and previous simulations a decoupling of oxygen and silicon dynamics is observed upon cooling. The origin of this decoupling is studied in the framework of the potential energy landscape. From analysis of the transition features between neighboring superstructures of minima, denoted metabasins, the differences between the oxygen and the silicon dynamics can be quantified. The decoupling can be explicitly related to the presence of generalized rotational processes, giving rise to oxygen but not to silicon displacement. Closer analysis of these processes yields important insight into the nature of the potential energy landscape of silica. The physical picture of relaxation processes in silica, obtained in previous work for the oxygen dynamics, is consistent with the decoupling effects, elucidated here.