First-principles study on the optical properties of KNbO₃

We report our studies on the electronic structure and linear and nonlinear optical (NLO) properties of KNbO₃ using a first-principles method in the local density approximation (LDA). The calculated results for the refractive indices and second-harmonic-generation (SHG) coefficients agree well with experimental results. From decomposing the nonlinear susceptibility, we find that the primary contribution to the NLO behaviour comes from the hybridization of the O 2p and Nb 4d electron states. In addition, there are two different roles played by the O atoms because of their different distances from the Nb atom; thus we propose a possible way to enhance the SHG coefficients.