Empirical three-body potential for vitreous silica

Abstract

A three-body potential suitable for molecular dynamics (MD) simulations has been developed for vitreous silica by adding three-body interactions to the Born–Mayer–Huggins (BMH) pair potential. Previous MD simulations with the BMH potential have formed glassy SiO2 through the melt-quench method with some success. Though bond lengths were found to be in fair agreement with experiment, the distribution of tetrahedral angles was too broad and the model glass contained 6%–8% bond defects. This is indicative of a lack of the local order that is present in the laboratory glass. The nature of the short range order is expected to play an important role when investigating defect formation, surface reconstruction, or surface reactivities. An attempt has been made to increase the local order in the simulated glass by including a directional dependent term in the effective potential to model the partial covalency of the Si–O bond. The vitreous state obtained through MD simulation with this modified BMH potential shows an increase in the short range order with a narrow O–Si–O angle distribution peaked about the tetrahedral angle and a low concentration of bond defects, typically ∼1%–2%. The static structure factor S(q) is calculated and found to be in good agreement with neutron scattering results. Intermediate range order is also discussed in reference to the distribution of ring sizes.