Recently it has been shown by the present author [H. Hasegawa, Phys. Rev. E 80 (2009) 011126] that the interpolation approximation (IA) to the generalized Bose–Einstein and Fermi–Dirac distributions yields good results in agreement with the exact ones within the O(q−1) and in high- and...

We compare the weakly inhomogeneous BCS-model of a previous investigation with a weak perturbation of a symmetrized Hubbard model in the pair formalism on the homogeneous lattice. In terms of our operator algebraic discussion we prove the existence of unique limiting Gibbs states at fixed...

We present an algebra of the creation and annihilation operators for spin 12 fermions which avoid double occupancy of an orbital state. These fermions, called orthofermions, obey the quantum statistics in which the state vector is antisymmetric only for the exchange of the orbital indices....

Thermodynamical properties of canonical and grand-canonical ensembles of the half-filled two-site Hubbard model have been discussed within the framework of the nonextensive statistics (NES). For relating the physical temperature T to the Lagrange multiplier β, two methods have been adopted:...

Ground-state structural transitions in finite-sized systems are studied in the Hubbard model. We use the concept of an effective temperature γ that is directly related to the interactions among electrons. We have studied all the possible clusters, with nearest-neighbour hopping, for two, three...

The magnetization and the electron number at the edge site are analytically calculated in the repulsive Hubbard model with a small magnetic field near the half-filling. Such quantities in the strong-coupling limit are evaluated. The relationship between the repulsive and the attractive Hubbard...

In 1968 we published the solution of the ground state energy and wave function of the one-dimensional Hubbard model, and we also showed that there is no Mott transition in this model. Details of the analysis have never been published, however. As the Hubbard model has become increasingly...

We use the doped Fullerenes as an example of how realistic systems can be described by simple models. Starting from the band structure we set up a tight-binding model that describes the t1u conduction band. Adding correlation terms we arrive at a generalized Hubbard Hamiltonian that we treat...

We present an exact diagonalization study of the half-filled Hubbard model on bipartite quasi-one-dimensional lattices. In particular, we emphasize the dependence of the ferrimagnetic ground state properties, and its associated magnetic excitations, on the Coulomb repulsion U.

Properties of the one-dimensional Hubbard model with a boundary field are studied. The present model realizes a strongly correlated electron system with almost localized impurity spins at the boundary. Physical quantities of the present model, e.g. the compressibility, the susceptibility and the...