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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.

Three SrTiO3 phases (cubic, tetragonal antiferrodistortive and tetragonal ferroelectric) are studied at the ab initio level. Lattice dynamics was calculated via the PBE0 and B3PW hybrid DFT exchange-correlation functionals within the LCAO formalism using the direct frozen-phonon method. The soft-mode-induced phase transitions and thermodynamics (heat capacity and Helmholtz free energy) are discussed. The results obtained are in good agreement with experiments, except for reproduction of the phase transition temperature. The study represents an important first step in considering defective and more complicated perovskite systems.

The results of the first-principles simulations of water adsorption on (001) surface of both cubic and orthorhombic phases of SrHfO3 crystal are presented. The dissociative and molecular water adsorption is investigated. The role of geometrical and chemical-bonding factors in the relative stability of different adsorption structures is discussed. A symmetry reducing from cubic to orthorhombic is shown to provide more optimal mutual orientation of adsorbate species thus increasing the water adsorption energy on the orthorhombic crystal compared with the cubic one.

HF-DFT LCAO hybrid simulations on (0 0 1) and (1 1 0) surfaces of orthorhombic and (0 0 1) surface of cubic SrHfO 3 perovskite are performed using a single slab model framework. PBE0 exchange-correlation functional is used for this study. The energy and crystal structure of bulk cubic and orthorhombic phases are calculated and compared. It is found that orthorhombic modification is more stable than cubic one by 24 kJ mol –1 per formula unit. Calculated average surface energies and relaxation energies proved to be similar for all orthorhombic surfaces. Atomic displacements along the direction normal to the surface are primarily determined by the type of termination and weakly depend on the surface indices. Without symmetry constraining, cubic surfaces are unstable with respect to reconstruction to corresponding orthorhombic surfaces at T = 0 K. While the upright displacements of the topmost atoms are mainly due to additional distortions of the surface octahedra, the lateral atomic displacements are closely related to changing in surface group tilting. The approach for the analysis of surface octahedron tilting is proposed and applied to the relaxed orthorhombic surfaces of SrHfO 3 perovskites. It is shown that the HfO 5 group on the HfO 2 -termianted surfaces undergoes a considerable turn upon relaxation, resulting in alignment of Hf–O–Hf bonds to corresponding pseudo-cubic directions.

Combining group-theoretical analysis and first-principles density functional theory calculations, we confirm theoretically the antiferrodistortive phase transition in ultrathin SrTiO${}_{3}$ (001) TiO${}_{2}$-terminated films and compare it with a similar transition in the bulk. We demonstrate phonon softening at the $M$ point of the surface Brillouin zone and analyze the change in the calculated electronic and phonon properties upon phase transition.

the Jahn–Teller effect occurs, thus reducing the cubic symmetry of a perfect crystal and leading to the appearance of both Raman- and infrared-active vibrational modes. The calculated phonon densities of states and group-theoretical analysis of defect-induced phonon frequencies were used for the interpretation of the relevant experimental data, once defect-induced local modes are identified. The temperature dependence of the Vo formation energy based on the calculated Gibbs free energy was also compared with experiments, and the phonon contribution therein estimated.

The combined use of ab initio quantum mechanical and x-ray absorption near edge structure (XANES) methods confirms that the oxygen vacancies (VO) are located in the first coordination shell of Fe3+ ions in the cathodic region of electrocolored Fe3+-doped SrTiO3. The binding energy of such a complex is estimated as ∼0.4 eV. The lattice distortions obtained in ab initio modeling and extended x-ray absorption fine structure experiments are in agreement. The predicted distortions make a minor effect on a simulated XANES signal, and its shape mainly depends on the presence of VO in the Fe3+ first coordination shell. Additionally, formation of the Fe3+–VO complex leads to disappearance of the phonon frequencies in the range of 620–760 cm−1 of the calculated phonon spectrum.

The results of hybrid density functional theory calculations on phonons in Sr(Fe(x)Ti(1-x))O(3) solid solution within the formalism of a linear combination of atomic orbitals are presented. The phonon density of states (DOS) calculated for 6.25% Fe(4+) impurities is reported and defect-induced phonon modes are identified. Based on our calculations and group-theoretical analysis, we suggest for the first time an interpretation of experimentally observed Raman- and IR-active modes.

Hybrid HF-DFT LCAO simulations of (001) surface properties and water adsorption on cubic SrTiO3, SrZrO3, and SrHfO3 perovskites are performed in a single-slab model framework. The optimized atomic structures and water adsorption energies have been calculated for a single water molecule per the surface unit cell. The possibility of the water molecular dissociation was investigated. Basing on the experimental data and results of the ab initio calculations the new interatomic potentials have been developed to describe the bulk and surface properties of the binary and ternary titanium and zirconium oxides. The proposed force-field takes into account the polarization effects via the shell model. The force-field suggested was used in the molecular mechanics calculations with the extended unit cells to study the possible surface reconstruction upon relaxation and hydroxylation of cubic perovskites.