Mechanism for linear and nonlinear optical effects in LiB3O5, CsB3O5, and CsLiB6O10 crystals

Electronic structure calculations of LiB3O5, CsB3O5, and CsLiB6O10 crystals from first principles are performed based on a plane-wave pseudopotential method. The static second-harmonic generation (SHG) coefficients are calculated at the independent-particle level with a formalism improved by our group and co-workers [Phys. Rev. B 60, 13 380 (1999)]. A real-space atom-cutting method is adopted to analyze the respective contributions of the cation and anionic groups to optical response. The calculated refractive indices and SHG coefficients are in good agreement with the experimental values. On the basis of these calculations, the influence of the cations on the band gaps and the optical responses is evaluated. The results show that with the increase of their radius their contributions to SHG become slightly more pronounced.