Influence of crystal structure and quasiparticle effects on second-harmonic generation: Silicon carbide polytypes

We report numerical calculations of the frequency-dependent second-order optical susceptibility for different polytypes of silicon carbide. The atomic and electronic structures are taken from first-principles calculations. We combine the plane-wave-pseudopotential method with the generalized tetrahedron method to compute the second-order coefficients. The influence of crystal structure as well as of many-body effects due to quasiparticle corrections is discussed in detail. Full frequency dependent spectra are calculated including quasiparticle corrections beyond scissors operator approximation.