CLUSTER-MODELS OF BULK, SURFACE, AND IMPURITY STRUCTURE IN ALPHA-ALUMINA

Self-consistent field embedded cluster models have been used to study the electronic structure of bulk, surface, and impurity regions of alpha-alumina, Al2O3. First principles local density (LD) theory is used to make an expansion of one-electron wave functions in a linear combination of atomic orbitals which permits direct interpretation of bonding and effective atomic configurations. The clusters are embedded self-consistently in the host lattice, so that all long-range potential effects are properly included. The LD calculations give a reasonably good account of bulk cohesion and bond length; relative energies of several cleavage faces are predicted. The nature of surface states for different terminating surfaces is examined, and results of partial relaxation ''experiments'' are reported. Local densities of state of Ti, Cr, and Fe substitutional impurities are discussed.