Computer modeling of natural silicate melts: what can we learn from ab initio simulations

TL;DR

This study compares ab initio and classical simulations of silicate melts, revealing that while structural parameters agree well, dynamical properties and infrared spectra are more accurately captured by ab initio methods.

Contribution

It demonstrates the advantages of ab initio molecular dynamics over classical force fields in modeling silicate melt properties, especially electronic polarization effects.

Findings

Structural parameters agree between methods

Ionic diffusivities are more sensitive to interaction details

Electronic polarization significantly affects infrared spectra

Abstract

The structural and dynamical properties of four silicate liquids (silica, rhyolite, a model basalt and enstatite) are evaluated by ab initio molecular dynamics simulation using the density functional theory and are compared with classical simulations using a simple empirical force field. For a given composition, the structural parameters of the simulated melt vary little between the two calculations (ab initio versus empirical) and are in satisfactory agreement with structure data available in the literature. In contrast, ionic diffusivities and atomic vibration motions are found to be more sensitive to the details of the interactions. Furthermore, it is pointed out that the electronic polarization, as evaluated by the ab initio calculation, contributes significantly to the intensity of the infrared absorption spectra of molten silicates, a spectral feature which cannot be reproduced using nonpolarizable force field. However the vibration modes of TO4 species and some structural details are not accurately reproduced by our ab initio calculation, shortcomings which need to be improved in the future.