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

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

Electron Correlations in Narrow Energy Bands: Ground State Energy and Metal-Insulator Transition

The electron correlations in narrow energy bands are examined in framework of the Hubbard model. The single-particle Green function and energy spectrum are obtained in paramagnetic state at half-filling by means of new two-pole approximation. In the ground state analitical expressions for the energy gap, polar states concentration and energy of the system are found. Metal-insulator transitions in the model at change of bandwidth or temperature are investigated. The obtained results are used for interpretation of some experimental data in narrow-band materials.Comment: 12 pages, 11 eps figures, Latex 2.0

Pressure-Temperature Phase Diagram of Generalized Hubbard Model with Correlated Hopping at Half-Filling

In the present paper pressure-temperature phase diagram of a generalized Hubbard model with correlated hopping in a paramagnetic state at half-filling is determined by means of the generalized mean-field approximation in the Green function technique. The constructed phase diagram describes metal-to-insulator transition with increasing temperature, and insulator-to-metal transition under the action of external pressure. The phase diagram can explain paramagnetic region of the phase diagrams of some transition metal compounds. We have found that taking into account correlated hopping allows much better description of these experimental data than the Hubbard model; this testifies also much better physics of the present model and the important role of correlated hopping.Comment: 7 pages, Latex 2.09 using Cond. Matt. Phys. style, submitted to Condensed Matter Physic