A MOLECULAR-MODEL FOR STRONGLY CORRELATED ELECTRON-SYSTEMS

We present exact results for a diatomic molecule described by the Ande rson model which includes both on-site and intersite hybridization, as well as the on-site Coulomb repulsion between f- and conduction elect rons (the Falicov-Kimball term). The mixed valence behaviour is demons trated in the subspace with N = 2 electrons, while the competition bet ween Kondo screening and RKKY interaction is investigated for N = 4 el ectrons. The Falicov-Kimball term restricts the range of stability of the mixed valence state, and increases the values of the Kondo tempera ture and of the crossover temperature to disordered f-moments in the K ondo and RKKY regime, respectively, while it increases the temperature above which the ferromagnetic correlations between f-moments are dest abilized for N = 3 electrons.