First-principles calculations of nonlinear optical susceptibility of inorganic materials

A method for calculations of the frequency-dependent nonlinear susceptibili ty of inorganic materials is implemented in the velocity gauge using a line ar combination of atomic orbitals (LCAO) method within the framework of eit her the Hartree-Fock approximation or density functional theory. It is base d on the standard time-dependent diagrammatic perturbation theory and has p reviously been applied successfully for atoms and molecules. For inorganic materials, it requires the eigenvalues and position operator matrix element s at several Ic points in the Brillouin zone. A quantitative assessment of the predictability of the method was made on cubic GaN for which the result s of previous theoretical studies are available.