Bond-orbital model for second-order susceptibilities

The bond-orbital model (BOM) for tetrahedral compounds is used self-consistently to calculate the second-order susceptibility. No adjustable parameters are used and agreement with experiment is good. The origin of the nonlinearity arises from a charge transfer as a result of the asymmetric polar energy between the anion and the cation. The model correctly predicts an optimum polarity to maximize second-order susceptibilities.