Valence fluctuation and phase transitions in a system of strongly interacting fermions

The effective Hamiltonian for the spinless generalized Falicov-Kimball model is obtained using a unitary transformation and Hubbard representations for the fermion operators. The electron phase transitions, depending on the position of f-level as well as on concentration of fermions, is investigated for arbitrary sign of intraatomic s-f interaction taking into account strong correlation between localized f and broad conduction s-states. ((orig.))