CORUNDUM BY DENSITY FUNCTIONAL THEORY AND HARTREE-FOCK CALCULATIONS. Karlheinz Schwarz, Peter Blaha, Technische Universität Wien, A-1060 Vienna, Getreidemarkt 9/158, Austria, Roberto Dovesi, Department of Inorganic, Physics and Materials Chemistry, University of Torino, via Giuria 5, I-10125 Torino, Italy
Corundum, or [[alpha]]-Al2O3, is investigated by two ab initio methods, namely the linearized augmented plane wave (LAPW) method as embodied in the WIEN95 code, and the periodic Hartree-Fock (HF) LCAO scheme using the CRYSTAL program. In density functional theory (DFT) both, the standard local density approximation (LDA) and the more sophisticated generalized gradient approximation (GGA) are used. With these methods we study DFT vs HF, LDA vs GGA, different basis sets (analytic vs numerical) and numerical differences involved in WIEN95 and CRYSTAL.
We investigate the electronic structure and will show the band structure and density of states and discuss chemical bonding. We optimize the structure which agrees well with the experimental geometry for which the electron density and the corresponding static structure factors are obtained by all schemes mention above. The small variations in the electron density caused by these schemes can be visualized by difference electron densities. These state-of-the-art results provide a good basis for a comparison with experimental structure factors and density distributions.
The electric field gradient (EFG) is extremely sensitive to the anisotropy of the charge density distribution and can be obtained directly from it. The theoretical results agree well with experimental EFGs.