On the Neglect of Local Coulomb Interaction on Oxygens in Perovskites Described by the Multi-band d−pd-p Model

On the example of TiO$_4$ layer (such as realized in Sr$_2$TiO$_4$) we study electronic structure of multi-band $d-p$ models describing transition metal perovskites. In agreement with the experiment, the studied system is predicted to be a robust nonmagnetic insulator. A realistic treatment of electronic structure requires one to introduce non-zero Coulomb local interactions at $2p$ oxygen orbitals. However, up till now majority of papers based upon multi-band models made an approximation of neglecting such interactions. We show that this simplification does not lead to serious problems in predictions of the electronic structure provided the Coulomb interactions at titanium ions and charge transfer gap are suitably renormalized (so they become entirely different with respect to the true microscopic $d-p$ model parameters).Comment: 1 figure, Physics of Magnetism 2017, Pozna\'n, June 201

On the correllation effect in Peierls-Hubbard chains

We reexamine the dimerization, the charge and the spin gaps of a half-filled Peierls-Hubbard chain by means of the incremental expansion technique. Our numerical findings are in significant quantitative conflict with recently obtained results by M. Sugiura and Y. Suzumura [J. Phys. Soc. Jpn. v. 71 (2002) 697] based on a bosonization and a renormalization group method, especially with respect to the charge gap. Their approach seems to be valid only in the weakly correlated case.Comment: 7pages,4figures(6eps-files

Ground-state properties of rutile: electron-correlation effects

Electron-correlation effects on cohesive energy, lattice constant and bulk compressibility of rutile are calculated using an ab-initio scheme. A competition between the two groups of partially covalent Ti-O bonds is the reason that the correlation energy does not change linearly with deviations from the equilibrium geometry, but is dominated by quadratic terms instead. As a consequence, the Hartree-Fock lattice constants are close to the experimental ones, while the compressibility is strongly renormalized by electronic correlations.Comment: 1 figure to appear in Phys. Rev.

Interrelation between the Optical Conductivity and Crystal Field Splitting in Monolayer Manganites

We introduce an effective model for correlated $e_g$ electrons which reproduces qualitatively the evolution of magnetic order in monolayer manganites when correlated wave functions are used. Here we address recent optical conductivity measurements suggesting that the splitting between the occupied and empty $e_g$ states is very large in $LaSrMnO_4$, contrary to what is expected for the effective model. We argue that no contradiction was found but several simple-minded one-atom-based expectations concerning crystal-field splitting and optical conductivity are in error

The Novel Spin-Charge Patterns in Correlated Electron Systems Described by Extended Hubbard Hamiltonian

Inhomogeneous spin and charge orderings in doped two-dimensional correlated electron systems described by the extended Hubbard Hamiltonian were investigated. At the crossover from stripe phases to charge order phases, the novel types of ordering connected with highly symmetric superlattice-type spin and charge patterns were identified. In particular, the emergence of local hexagonal-like symmetry is of interest as such patterns are generic in complex, nonlinear dynamic systems

The Novel Spin-Charge Patterns in Correlated Electron Systems Described by Extended Hubbard Hamiltonian

Inhomogeneous spin and charge orderings in doped two-dimensional correlated electron systems described by the extended Hubbard Hamiltonian were investigated. At the crossover from stripe phases to charge order phases, the novel types of ordering connected with highly symmetric superlattice-type spin and charge patterns were identified. In particular, the emergence of local hexagonal-like symmetry is of interest as such patterns are generic in complex, nonlinear dynamic systems

Stripe Phases in the Hubbard Model

We investigate the magnetic and charge ordering in the stripe phases obtained while using correlated wave functions for finite 8×8 clusters described by the Hubbard model with extended hopping. Nonmagnetic vertical (01) site-centered domain walls and (11) bond-centered stripes are found for the parameters of La$\text{}_{2-x}$Sr$\text{}_{x}$CuO$\text{}_{4}$ and YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+x}$, respectively, at doping δ=1/8. The obtained half-filled domain nonmagnetic walls reproduce the maxima observed in neutron scattering for La$\text{}_{2-x}$Sr$\text{}_{x}$CuO$\text{}_{4}$