Si–O–Si bond angle and torsion angle distribution in vitreous silica and sodium silicate glasses

Si–O–Si bond angle distribution (BAD) and torsion angle distribution (TAD) of vitreous silica and sodium silicate glasses have been studied using molecular dynamics simulation, and compared extensively with experimental and computational data. Correlations were investigated between the two angle distributions and the shoulder at 3.7 Å in total correlation function. Analysis of the simulated glass structures shows that, because TAD has preference for staggered configurations at low Si–O–Si angles due to steric effects, the shoulder is mainly associated with the width of the BAD. Whereas a smooth shoulder at 3.7 Å with a stagger-preferred TAD indicates a broad Si–O–Si BAD for vitreous silica, an emerging hump at 3.7 Å reveals the narrowing of the BAD on adding sodium. Finally, various Si–O–Si BADs from the literature are analyzed and a model for the BAD is proposed.