We compare two approaches to the atomic, electronic, and magnetic structures of LaMnO 3 bulk and the ͑001͒, ͑110͒ surfaces-hybrid B3PW with optimized LCAO basis set ͑CRYSTAL-2003 code͒ and GGA-PW91 with plane-wave basis set ͑VASP 4.6 code͒. Combining our calculations with those available in the literature, we demonstrate that combination of nonlocal exchange and correlation used in hybrid functionals allows to reproduce the experimental magnetic coupling constants J ab and J c as well as the optical gap. Surface calculations performed by both methods using slab models show that the antiferromagnetic ͑AF͒ and ferromagnetic ͑FM͒ ͑001͒ surfaces have lower surface energies than the FM ͑110͒ surface. Both the ͑001͒ and ͑110͒ surfaces reveal considerable atomic relaxations, up to the fourth plane from the surface, which reduce the surface energy by about a factor of 2, being typically one order of magnitude larger than the energy difference between different magnetic structures. The calculated ͑Mulliken and Bader͒ effective atomic charges and the electron density maps indicate a considerable reduction of the Mn and O atom ionicity on the surface.

The atomic, electronic structure and phonon frequencies have been calculated in a cubic and low-temperature tetragonal SrTiO 3 phases at the ab initio level. We demonstrate that the use of hybrid exchange-correlation PBE0 functional gives the best agreement with experimental data. The results for the standard PBE and hybrid PBE0 are compared for the two types of basis sets: a linear combination of atomic orbitals (LCAO, CRYSTAL09 computer code) and plane waves (PW, VASP 5.2 code). Relation between cubic and tetragonal antiferrodistortive (AFD) phases and the relevant AFD phase transition observed at 110 K is discussed in terms of group theory and illustrated with analysis of calculated soft mode frequences at the Γ and R points in the Brillouin zone. Based on phonon calculations, the temperature dependences of the Helmholtz free energy and heat capacity are in a good agreement with experiment.

Using a hybrid Hartree–Fock (HF)-DFT method combined with LCAO basis set and periodic supercell approach, the atomic, electronic structure and phonon properties of oxygen vacancies in ZnO and SrTiO3 were calculated and compared. The important role of a ghost basis function centered at the vacant site and defect spin state for SrTiO3 is discussed. It is shown that the use of hybrid functionals is vital for correct reproduction of defects basic properties. The Gibbs free energy of formation of oxygen vacancies and their considerable temperature dependence has been compared for the two oxides. These calculations were based on the polarizability model for the soft mode temperature behavior in SrTiO3. The supercell size effects in the Gibbs free energy of formation of oxygen vacancies in the two oxides are discussed. The major factors for the quite different behavior of the two oxides and the degree of electron delocalization nearby the oxygen vacancy have been identified.