Energy-Band Structure of SrTiO3from a Self-Consistent-Field Tight-Binding Calculation

Energy bands of SrTi${\mathrm{O}}_3$ have been computed ab initio using a nonrelativistic self-consistent-field (SCF) procedure based upon the linear-combination-of-atomic-orbitals or tight-binding formalism. A slightly extended multicentered-atomic-orbital basis was used and integrals over them were evaluated in keeping with the Hartree-Fock-Roothaan procedures. Three- and four-centered integrals were treated by previously justified numerical approximations. Results are in good agreement with experimental evidence for the ordering and widths of the valence and conduction bands. A 12.1-eV band gap was obtained, however, from the ground-state SCF results. Consideration of various energy terms and comparison with an independent SCF calculation on the isolated Ti${\mathrm{O}}_6^{-8\mathrm{}}$ cluster confirm Šimánek and Šroubek's earlier criticism of Kahn and Leyendeker's semiempirical model and suggest significant hole-particle correlation in the electronically excited states of the crystal. Though by a less rigorous analysis, the Sr orbital interactions are judged not to perturb the features of these results.