An ab initio pseudopotential calculation of ground-state and excited-state properties of gallium nitride

In this work, the electronic, ground-state and vibrational properties of both alpha -GaN (i.e. wurtzite structure) and the recently fabricated beta -GaN (i.e. zincblende structure) have been studied using the ab initio pseudopotential method within the local density approximation and a simple quasi-particle scheme. The calculated equilibrium lattice constants, bulk moduli, the pressure derivatives of the bulk moduli, and the Al TO( Gamma ) phonon frequency are in good agreement with available experimental and other recent ab initio theoretical results. The self-energy band gap corrections are found to be highly k-dependent. The calculated fundamental band gap is direct in both cases and for the experimental lattice constant is calculated to be 3.36 eV in beta -GaN and 3.48 eV in alpha -GaN, in excellent agreement with experiment.