Dynamics of SiO$_2$ glasses

TL;DR

This paper investigates the vibrational and relaxation dynamics of silica glasses using molecular dynamics, analyzing structures, eigenmodes, and relaxation types to understand atomic displacements and bond-breaking processes.

Contribution

It provides a detailed molecular dynamics analysis of silica glass vibrations and relaxations, highlighting the nature of relaxation mechanisms and eigenmode structures.

Findings

Vibrational density of states characterized for silica glasses.

Relaxations involve both small displacements and bond-breaking.

Eigenvectors of relaxations resemble low-frequency vibrational modes.

Abstract

Results on the dynamics of silica are presented: vibrations and relaxations. Using molecular dynamics, glass structures are generated by rapidly quenching melts below the glass transition. For the local minima of the structures the vibrational density of states is determined, the structures of the eigenmodes are analyzed, and the influence of the single components is discussed. Relaxations are studied in both amorphous SiO$_2$ and silica melts. Our main focus is on the type of relaxation, i.e., whether the main contributions are caused by small atomic displacements, or by bond-breaking processes, e.g. creation and annihilation of dangling bonds. The eigenvector of the relaxations is found to be similar to the low-frequency one.