First-principle calculations of the dielectric function of zinc-blende and wurtzite InN

The imaginary part of the dielectric function of zinc-blende and wurtzite InN has been calculated using a full-potential linearized augmented plane wave method. We show that the exchange potential of Engel and Vosko gives an insulating ground state for both structures. The real part of the dielectric function has been obtained from the Kramers-Kronig dispersion relations, assuming a quasiparticle band-gap correction according to Bechstedt and Del Sole. We have found that it is necessary to have a good account of the band gap in order to derive the low-frequency optical properties. We present the longitudinal as wen as the transverse components in wurtzite InN, showing that the anisotropy is small.