Characterizing MRO in atomistic models of vitreous SiO$_2$ generated using ab-initio molecular dynamics

TL;DR

This paper uses ab-initio molecular dynamics to generate atomistic models of vitreous silica, analyzing their structural and electronic properties, including defect states and the impact of various vacancies on the electronic band-gap.

Contribution

It introduces a melt-quench AIMD approach to model vitreous silica and provides a detailed comparison with experimental data and previous models, focusing on electronic and structural defects.

Findings

Presence of defect states due to dangling bonds in the band-gap

Edge-shared defective structures contribute to the valence band

Oxygen and Silicon vacancies influence the band-gap

Abstract

Vitreous silica is the most versatile material for scientific and commercial applications. Although large-scale atomistic models of vitreous-SiO$_2$ (v-SiO$_2$) having medium-range order (MRO) have been successfully developed by melt-quench through classical molecular dynamics, the MRO is not well studied for the smaller-scale models developed by melt-quench using ab-initio molecular dynamics (AIMD). In this study, we obtain atomistic models of v-SiO$_2$ by performing melt-quench simulation using AIMD. The final structure is compared with the experimental data and some recent atomistic models, on the basis of the structural properties. Since AIMD allows for the estimation of electronic structure, a detailed study of electronic properties is also done. It shows the presence of defect states mainly due to dangling bonds in the band-gap region of electronic density of states, whereas the edge-shared type of defective structures in the glassy models are found to contribute mainly in the valence band. In addition, Oxygen and Silicon vacancies as well as bridging Oxygen type of defects were created and their contributions to the band-gap were studied.