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 alp ha-alumina, Al2O3. First principles local density (LD) theory is used to make an expansion of one-electron wave functions in a linear combin ation of atomic orbitals which permits direct interpretation of bondin g and effective atomic configurations. The clusters are embedded self- consistently in the host lattice, so that all long-range potential eff ects are properly included. The LD calculations give a reasonably good account of bulk cohesion and bond length; relative energies of severa l cleavage faces are predicted. The nature of surface states for diffe rent terminating surfaces is examined, and results of partial relaxati on ''experiments'' are reported. Local densities of state of Ti, Cr, a nd Fe substitutional impurities are discussed.