ORBITAL LOCALIZATION AND DELOCALIZATION EFFECTS IN THE U-5F(2) CONFIGURATION - IMPURITY PROBLEM

Anderson models, based upon quantum chemical studies of the molecule u ranocene U(C8H8)(2), are applied to investigate the problem of an U im purity in a metal. The special point here is that the U 5f orbitals ar e divided into two subsets: an almost completely localized set and a c onsiderably delocalized one. Due to the crystal field, both localized and delocalized U 5f orbitals affect the low-energy physics. A numeric al renormalization-group study shows that every fixed point is charact erized by a residual local spin and a. phase shift. The latter changes between 0 and pi/2, which indicates the competition between two diffe rent fixed points. Such a competition between the different local spin s at the fixed points reflects itself in the impurity magnetic suscept ibility. These different features cannot be obtained if the mixed loca lized/delocalized character of U 5f orbitals is neglected. [S0163-1829 (98)04117-4].