A periodic ab initio extended basis set study of α-Al₂O₃

Corundum, or α-Al2O3, is investigated at the ab initio periodic Hartree-Fock LCAO level using the program CRYSTAL. A split valence 6–21G basis set is adopted, and the influence of d polarization functions is explored. The four geometrical parameters of the unit cell are optimized, the difference with respect to the experimental data always being less than 1%. The electric field gradient tensor at both nuclei (Al and O) is calculated; agreement with the experimental data is quite satisfactory. Band structure, density of states and charge density maps are also given. The resulting electronic structure is highly ionic.