The ground state of dilute Tm, Pr, and U systems is degenerate

The ground state of the appropriate generalization of the impurity Anderson model for valence fluctuations between two realistic configurations, is obtained in the atomic, narrow-band limit, using the Lanczos method. This limit describes the strong-coupling fixed point of renormalization group treatments for intermediate valence and Kondo impurities. The resulting ground state of Tm is highly degenerate and contains states of total angular momentum 0, 3/2, 2, 5/2, 4 and 9/2. The ground state of Pr has Jt=15/2 and that of U has Jt=8. For Tm, the crystal electric field or and an applied magnetic field should split the degeneracy favouring the magnetic states. In agreement with experiments in Tm and U compounds the magnetic moment at the impurity is in all cases anomalously small. It decreases when L-S coupling is replaced by intermediate coupling and vanishes in the limit of j-j coupling. (orig.)