A study of the bulk optical and electronic properties of a thin film semiconductor as a function of the variation of the lattice parameter using time dependent current density functional theory

First principles studies have been performed on the zinc-blende and rocksalt structures of gallium nitride (GaN) within the time dependent current density functional theory (TDCDFT) regime via the implemented Vignale-Kohn polarization functional [P. Romaniello and P. L. de Boeij, Phys. Rev. B, 71, 155108, (2005)].;Ab initio calculations of the pseudodielectric function &egr;(o)=&egr; 1(o)+i&egr;2(o) of zinc-blende and rocksalt GaN were performed within the range of 1.5-5.0 eV and 0-10 eV, respectively, as a function of the compression and expansion of their lattice constants +/-5%. The strained density of states and the imaginary part of the pseudodielectric function [&egr;2(o)] were investigated and contrasted against the unstrained system. The derived optical constants, reflectivity and refractive index and the effect of strains on the polytypes were also studied. The results are in reasonable agreement with previous theoretical and experimental findings of both polytypes.