Steric origin of the silicon-oxygen-silicon angle distribution in silica

The oxygen-oxygen separation distance between adjacent tetrahedra in silica has been considered as a restrictive criterion for the formation of accepted structures. The single stipulation of a minimum O-O separation of say 2.9 Å leads to a distribution of the Si-O-Si angle with a maximum at about 145° and cutoffs near 120° on the low end and 180° on the high end of the scale, all in excellent agreement with the experimental observations for silica. No detailed energetic considerations are involved.