Mechanism for linear and nonlinear optical effects in monoclinic bismuth borate (BiB3O6) crystal

Electronic structure calculations of BiB3O6 crystal from first principles are performed based on a plane-wave pseudopotential method. The linear refractive indices and the static second-harmonic generation (SHG) coefficients are also calculated by the SHG formula improved by our group. The calculated values are in good agreement with the experimental values. A real-space atom-cutting method is adopted to analyze the respective contributions of the cation and anionic groups to the optical response. The results show that the contribution of the (BiO4)5− anionic group to the SHG coefficients is more pronounced than that of the (BO3)3− and (BO4)5− groups.