Photoelasticity of sodium silicate glass from first principles

TL;DR

This study uses first-principles density-functional perturbation theory to compute the photoelastic tensor of sodium silicate glass, successfully matching experimental data and revealing the structural factors influencing photoelastic response.

Contribution

It provides the first-principles calculation of sodium silicate glass's photoelastic tensor and extends a phenomenological model to explain Na's effect on photoelasticity.

Findings

Calculated photoelastic coefficients agree with experiments

Na insertion decreases photoelastic response quantitatively

Modulation of structural parameters beyond SiOSi angles affects photoelasticity

Abstract

Based on density-functional perturbation theory we have computed the photoelastic tensor of a model of sodium silicate glass of composition (Na$_2$O)$_{0.25}$(SiO$_2$)$_{0.75}$ (NS3). The model (containig 84 atoms) is obtained by quenching from the melt in combined classical and Car-Parrinello molecular dynamics simulations. The calculated photoelastic coefficients are in good agreement with experimental data. In particular, the calculation reproduces quantitatively the decrease of the photoelastic response induced by the insertion of Na, as measured experimentally. The extension to NS3 of a phenomenological model developed in a previous work for pure a-SiO$_2$ indicates that the modulation upon strain of other structural parameters besides the SiOSi angles must be invoked to explain the change in the photoelstic response induced by Na.