STRUCTURE AND ENERGETICS OF ALUMINA SURFACES CALCULATED FROM FIRST PRINCIPLES

First-principles calculations based on density-functional theory and pseudopotentials are used to calculate the energies and relaxed structures of five low-index surfaces of or-alumina. Evidence for the reliability of the theoretical methods is provided by calculations of the lattice parameters and internal coordinates of the perfect crystal, which agree very closely with experimental data. It is shown that, for some of the surfaces, relaxation effects reduce the surface energy by over a factor of two and lead to major changes of surface structure, with particularly large effects being found for the (0001) and (1010) surfaces. Results are also presented for the distribution of valence electron charge in the surface region. These results suggest that or-alumina is highly ionic even for ions at the surface.