Calculation of the nonlinear optical coefficient of the crystal

For the first time, we present the calculation of the nonlinear optical coefficient of the (NAB) crystal from a systematic and quantitative standpoint. Based on the dielectric theory of complex crystals and the Levine bond charge model, the method of calculation of the second-order nonlinear optical tensor coefficients of complex crystals has been given systematically. The chemical bond parameters and linear and nonlinear susceptibilities of the NAB crystal have been calculated in detail, and the calculated value of is esu, which agrees with the measured value of esu.