Calculated second-harmonic susceptibilities of BN, AlN, and GaN

We report calculations for the dielectric constant ε∞ and the second-harmonic susceptibility d for BN, AlN, and GaN in both zincblende and wurtzite structures within the Kohn–Sham local-density approximation. For wurtzite AlN and GaN, the computed dxxz(w) and dzzz(w) closely agree with experiment. For zincblende AlN and GaN as well as zincblende and wurtzite BN, we predict d. Our results show that the simple relation between the independent components of d predicted by bond additivity works for BN, breaks down for GaN, and completely fails for AlN.