Kuzian R. Modeling of physical properties of transition metal oxide compounds within the frameworks of microscopic generalized Hubbard model.

A systematic approach for the modelling of transition metal oxides is proposed. For paramagnetic impurities in wide-gap semiconductors the connection of effective spin-Hamiltonian with the local electronic structure is shown. The superexchange interaction between the impurities is calculated. The geometry of d-orbitals, Hubbard and Hund interactions are taken into account. A possibility of Lieb-Mattice ferrimagnetic superstructure formation for arbitrarily low concentration of magnetic impurities in semiconductors is shown. Frustrated magnetism in edge-shared cuprates is studied: the results of inelastic neutron scattering are unambiguously interpreted for materials with competing interactions; exact one- and two-particle excitation spectra of acute-angle helimagnets above their saturation magnetic field are found; analytic expressions for the saturation magnetic field value are obtained, it takes into account interchain couplings and the exchange interactions anisotropy; the temperature dependence of resonant inelastic X-ray scattering spectra are explained. The one-step theory of angle-resolved photoemission is developed for the basis of localized orbitals. For the simplest case of a one-band Mott-Hubbard system and neglecting the modification of the crystal potential at the surface we have obtained an analytical expression for the photocurrent assuming that the inelastic scattering in the final state can be described by a mean free path.