First-principles calculations of nonlinear optical susceptibility of inorganic materials

A method for calculations of the frequency-dependent nonlinear susceptibility of inorganic materials is implemented in the velocity gauge using a linear combination of atomic orbitals (LCAO) method within the framework of either the Hartree–Fock approximation or density functional theory. It is based on the standard time-dependent diagrammatic perturbation theory and has previously been applied successfully for atoms and molecules. For inorganic materials, it requires the eigenvalues and position operator matrix elements at several k points in the Brillouin zone. A quantitative assessment of the predictability of the method was made on cubic GaN for which the results of previous theoretical studies are available.