Four well known HF, LDA, GGA and B3LYP Hamiltonians in LCAO approximation were used in band structure calculations to obtain the main properties of the perfect GaN crystal with hexagonal lattice (C6v4 space group). Calculated lattice parameters, elastic constants and the band gap were compared with the experimental data and the results of other calculations. As a consequence, the GGA Hamiltonian was chosen, giving the lattice parameters a = 3.20Å, c = 5.20Å, u = 0.377, the bulk modulus B = 206GPa and the energy gap Eg = 2.7eV. These results reasonably reproduced the experimental data. For the point defects calculation (VGa, VN, MgGa, ZnGa, CN and SiN) the super-cell model was applied .The shape and size of super-cell influence on the results was investigated. It was found that a super-cell of 96 atoms ensured a reasonable agreement with the band structure calculations for perfect crystal and weak defect-defect interaction between the images of point defect in the periodic model.

LCAO Calculation of Neutral Defects in GaN. A.Gulans, R.A.Evarestov, I.Tale, C.C.Yang: Physica Status Solidi C, 2005, 2[7], 2525-8