AB-INITIO 2ND-HARMONIC SUSCEPTIBILITIES OF SEMICONDUCTORS - GENERALIZED TETRAHEDRON METHOD AND QUASI-PARTICLE EFFECTS

We report numerical calculations of the frequency-dependent second-ord er optical susceptibility. The results are based on an ab initio treat ment of the geometry and the electronic structure within the density-f unctional theory in local-density approximation. The plane-wave-pseudo potential method is combined with a generalized tetrahedron method to perform the k-space integration. The analytic linear tetrahedron metho d has to be improved because of the energy-dependent prefactors of the delta functions describing the energy conservation. We also present r esults for spectra of the second-harmonic generation where many-body q uasiparticle effects are included beyond the scissors-operator approxi mation. Zinc-blende semiconductors are considered as model substances.