Electronic structure of a grain-boundary model in SrTiO3

It is known that grain boundaries (GB's) in strontium titanate (SrTiO3) pla y an important and often a controlling role in determining the material's e lectrical properties. To understand how their electronic structures are rel ated to the GB structures, we have examined two structure models of the Sig ma 5 GB in SrTiO3 obtained by first-principles pseudopotential total energy calculations. The electronic structure of bulk crystal and the relaxed GB models are then studied by using the orthogonalized linear combination of a tomic orbitals method. Results are presented for the ground-state structura l properties and band structure of bulk SrTiO3, the total density of states (DOS), the atom and orbital-resolved partial DOS, effective charges, bond order, charge-density distribution, and near-edge structure of electron ene rgy-loss spectroscopy. It is shown that the GB structures have smaller valu es of fundamental band gaps, effective charges, and bond orders relative to bulk SrTiO3. There are no GB-induced electronic states within or at the ed ge of the fundamental band gap. The 100-atom GB model with buckled Sr colum ns in the GB con is found to be a more likely model. It is also shown that the electron charge distribution across the GB line in SrTiO3 is almost bal anced.