3d3d-electrons contribution to cohesive energy of 3d3d-metals

In this paper a model for $3d$-subsystem of transition $3d$-metals has been proposed and used for calculation of the cohesive energy dependent on $3d$-band filling of particular metal, its bandwidth and effective intra-atomic interaction value. It has been shown that the model enables one to explain the observed peculiarities of cohesive energy effect on the atomic number. The nature of two parabolic dependencies of cohesive energy on $3d$-band filling has been clarified. The calculated values of cohesive energy are close to those experimentally obtained for Sc-Ti-V-Cr-Mn-Fe series.Comment: 7 pages, 2 figures, 2 table

Phase Diagram of Metal-Insulator Transition in System with Anderson-Hubbard Centers

The model of a strongly correlated system in which periodically spaced Anderson-Hubbard centers are introduced into narrow-band metal is considered. Besides the interactions between localized magnetic moments and strong on-site Coulomb interaction, the model takes into account the hybridization of localized and band states. To study the efect of the lattice deformation on the electrical properties of the system the phonon term and elastic energy have been taken into account. Green functions for band and localized electrons have been found. On this base, the energy spectrum has been investigated as function of model parameters, temperature and external pressure. The criterion of metal-insulator transition for integer value of electron concentration has been derived and the phase diagram of the metal-insulator transition has been built.Comment: presented at 12 International Simposium on Physics of Materials, Prague 4-8.09.201

Some Low-Temperature Properties of a Generalized Hubbard Model with Correlated Hopping

In the present paper we study some correlation effects in a generalized Hubbard model with correlated hopping within low-temperature region using a generalized mean-field approximation. It is shown that in a series of cases the model leads to consequences deviating essentially from those of the Hubbard model. We consider the possibility of applying the result to interpret the peculiarities of physical properties of systems with narrow energy bands.Comment: 2 pages, LaTex2e using Elsevier style, presented at LT22 Conference, Helsinki, August 199

Ground state ferromagnetism in a doubly orbitally degenerate model

In the present paper the ground state of a double orbitally degenerate model at weak intra-atomic interaction is studied using the Green functions method. Beside the diagonal matrix elements of electron-electron interactions the model includes correlated hopping integrals and inter-atomic exchange interaction. The influence of orbital degeneracy with Hund's rule coupling, correlated hopping and inter-atomic direct exchange on the ferromagnetic ordering is investigated. The expressions for ground state energy and magnetization, the criterion of transition from paramagnetic to ferromagnetic ground state as functions of the model parameters are obtained. The obtained results are compared with some experimental data for magnetic materials.Comment: 13 pages, 11 eps figure

Magnetic field dependence of conductivity and effective mass of carriers in a model of Mott-Hubbard material

The influence of external magnetic field $h$ on a static conductivity of Mott-Hubbard material which is described by model with correlated hopping of electrons has been investigated. By means of canonical transformation the effective Hamiltonian which takes into account strong intra-site Coulomb repulsion and correlated hopping is obtained. Using a variant of generalized Hartree-Fock approximation the single-electron Green function and quasiparticle energy spectrum of the model have been calculated. The static conductivity $\sigma$ has been calculated as a function of $h$, electron concentration $n$ and temperature $T$. The correlated hopping is shown to cause the electron-hole asymmetry of transport properties of narrow band materials.Comment: 10 pages, 7 figures, submitted to Condensed Matter Physics journa