Hybrid DFT calculations of the atomic and electronic structure for ABO ₃ perovskite (0 0 1) surfaces

We present the results of first-principles calculations on two possible terminations of the (0 0 1) surfaces of SrTiO₃, BaTiO₃, and PbTiO₃ perovskite crystals. Atomic structure and the electronic configurations were calculated for different 2D slabs, both stoichiometric and non-stoichiometric, using hybrid (B3PW) exchange-correlation technique and re-optimized basis sets of atomic (Gaussian) orbitals. Results are compared with previous calculations and available experimental data. The electronic density distribution near the surface and covalency effects are discussed in details for all three perovskites. Both SrTiO₃ and BaTiO₃ (0 0 1) surfaces demonstrate reduction of the optical gap with respect to the bulk, especially for the TiO₂-terminated surfaces, whereas PbTiO ₃ surfaces show a slight increase of the gap. The top of the PbTiO₃ valence band lies at X point of the Brillouin Zone, unlike the M point for SrTiO₃ and BaTiO₃.