LCAO calculation of neutral defects in GaN

Four well known HF, LDA, GGA and B3LYP Hamiltonians in LCAO approximation have been used in band structure calculations to obtain the main properties of the perfect GaN crystal with hexagonal lattice (C_6v⁴ space group). Calculated lattice parameters, elastic constants and the band gap have been compared with the experimental data and the results of other calculations. As a consequence, the GGA Hamiltonian has been chosen, giving the lattice parameters a = 3.20 Å, c = 5.20 Å, u = 0.377, the bulk modulus B = 206 GPa and the energy gap E_g = 2.7 eV. These results reasonably reproduce the experimental data. For the point defects calculation (V _Ga, V_N, Mg_Ga, Zn_Ga, C_N, and Si_N) the supercell model was applied. The shape and size of supercell influence on the results was investigated. It was found that the supercell of 96 atoms ensures the reasonable agreement with the band structure calculations for perfect crystal and weak defectdefect interaction between the images of point defect in the periodic model.