Calculation of structural electronic and optical properties of gallium nitride

Full-potential linearized augmented plane-wave method (FP-LAPW) within the density functional theory is applied to study the structural electronic and optical properties of gallium nitride (GaN) in the Zinc-Blende (ZB) and Wurtzite (WZ) phase at high pressures. Local density approximation (LDA), generalized gradient approximation (GGA), an alternative form of GGA proposed by Engel and Vosko (EV-GGA) and modified Becke-Johnson (mBJ) have been used based on exchange-correlation energy optimization.The calculated energy allowed us to investigate several structural properties such as lattice parameter, bulk modulus and its pressure derivative.Our calculated lattice parameter is found to be in reasonable agreement with experimental result. The electronic band structure and the density of states at various pressures are also calculated to show that there is a possibility for these compounds to become semiconductors at high pressures. In the optical part, several optical quantities were investigated, in particular the inter band transitions have deduced from the imaginary part of the dielectric function.