Hopping perturbation treatment of the periodic Anderson model around the atomic limit

The periodic Anderson model with two strongly correlated subsystems of d and f electrons and local on-site hybridization is investigated by considering the hopping of d electrons between lattice sites as perturbation. In zero order without the intersite transfer term, the system of correlated d and f electrons can be treated exactly. The delocalization of electrons and the corresponding renormalization of the one-particle Green's functions are analyzed by using a special diagram technique from which the Dyson equations for the Green's functions are established. We discuss the physics of the delocalized electrons in the simplest approximation corresponding to a Hubbard I-like decoupling giving rise to eight different energy bands, which depend in a non-trivial way on the exact eigenvalues of the local model. These bands are discussed for the symmetrical case in which the energies of doubly occupied d and f states are equal to each other.