Quantum-chemical Approach to the Dependence of Oxygen Charge on Bond Angle in SiO2

A recently published review on the effective oxygen charge in SiO₂ and its dependence on the bond angle of oxygen has shown that, as a rule, solid-state theoretical calculations lead to the conclusion that the oxygen charge increases with increasing bond angle, whereas quantum-chemical calculations for limited clusters yield an opposite result, i.e. a decrease of the oxygen charge with increasing oxygen angle. In the present paper it is shown that also a quantum-chemical approach to the problem, namely a molecular-orbital calculation for an Si O Si bridge, reveals an increase of the charge of oxygen with its bonding angle, which is, however, relatively weak.