Ab initio calculations of the atomic and electronic structure of beta-silicon nitride

The atomic and electronic structure of the beta-silicon nitride (beta-Si3N4 ) crystal have been determined using the ab initio pseudopotential method b ased on the density functional theory. We have obtained the stable lattice parameters and the stable positions of 14 atoms in the unit cell for the st ructure P6(3)/m for the first time. The electronic structure and the charge distribution indicate that the Si-N bond has both ionic and covalent chara cters. The band structure is in good agreement with the other first-princip les results and consistent with the experiments.