The vibrational dynamics of vitreous silica: Classical force fields vs. first-principles

TL;DR

This study compares classical force field and first-principles methods for modeling the vibrational properties of vitreous silica, revealing significant differences and improvements in accuracy with ab initio relaxation.

Contribution

It demonstrates that ab initio relaxation significantly enhances the accuracy of vibrational density of states compared to classical force fields.

Findings

Ab initio relaxation improves agreement with experimental vibrational density of states.

Classical force fields can misrepresent vibrational mode nature in certain frequency ranges.

Differences between models highlight limitations of effective potentials for vibrational analysis.

Abstract

We compare the vibrational properties of model SiO_2 glasses generated by molecular-dynamics simulations using the effective force field of van Beest et al. (BKS) with those obtained when the BKS structure is relaxed using an ab initio calculation in the framework of the density functional theory. We find that this relaxation significantly improves the agreement of the density of states with the experimental result. For frequencies between 14 and 26 THz the nature of the vibrational modes as determined from the BKS model is very different from the one from the ab initio calculation, showing that the interpretation of the vibrational spectra in terms of calculations using effective potentials can be very misleading.