Electronic structure of pristine and solute-incorporated SrTiO3: I, perfect-crystal-geometry and acceptor doping

In Part I of this three-part report, various aspects of the electronic stru cture of pristine and acceptor-impurity-incorporated perfect-crystal SrTiO3 were investigated. An embedded-cluster approach was used to perform first- principles, self-consistent-field calculations. Within the framework of the local-density functional approximation, one-electron equations were evalua ted using a discrete variational method to study pristine titanium- and str ontium-centered clusters of perfect-crystal SrTiO3. Clusters with a single acceptor impurity substitution at the central titanium site also were consi dered. However, the relaxation of the atomic structure resulting from the i ncorporation of these single impurities were not considered in the calculat ions. Calculations involved determination of the densities of states and sp in densities of states of the cluster atoms near the Fermi energy, Mulliken charge populations of atomic orbitals, valence of individual atoms, and na ture of bonds between the atoms also were determined. Spatial distribution of charge density and spin density of valence band orbitals, which were inc luded in the variational space, were determined for pristine and impurity-c entered clusters. The influence of impurity substitution at a titanium site on the local electronic structure was evaluated in terms of the variations in the densities of states and in the spatial distribution of charge densi ties. The role of local charge transfer and impurity-induced changes in Mul liken populations also were investigated in connection with the electronic activity of SrTiO3. Possible mechanisms of electrical conductivity were stu died, Cluster calculations revealed a mixed ionic-covalent nature of the Ti -O bond and purely ionic nature of the Sr-O bond for the perfect-crystal ge ometry, of SrTiO3. The optical bandgap and the densities of states-calculat ed using the cluster method were in good agreement with previous theoretica l and experimental investigations. The methodology correctly predicted the acceptor nature and the trends therein of the transition-metal impurities a t the titanium sites. For pristine and impurity-incorporated clusters, the densities of states, the charge- and spin-density distributions, and the Mu lliken charge population consistently converged to the same results, provid ing information regarding the electronic behavior of the SrTiO3.