Effective oxygen charge in SiO2 and its dependence on the bond angle of oxygen

It is not clear until now, whether the oxygen bond angle and the effective oxygen charge in SiO₂ are correlated or not. This paper reviews various theoretical and experimental facts concerning some special features of the atomic structure and of electronic properties of SiO₂. They lead to contrary conclusions about the correlation between the effective oxygen charge and the oxygen bond angle in distinct SiO₂ forms. Results basing on quantum-chemical investigations are compared with conclusions drawn from the dielectric theory and from tight-binding calculations of electronic states. A critical valuation of the different methods with special consideration of solid-state investigations yield the result that the effective oxygen charge increases with increasing bond angle.