Correlation mechanism of the f-electron delocalization

The mechanism of f-electron delocalization is investigated within the multi-orbital Anderson lattice model by means of diagrammatic perturbation theory from the atomic limit. The derived equations couple the intra-atomic transition energies, their spectral weights and population numbers of the many-electron states. Its self-consistent solution for praseodymium metal shows that the delocalization can be caused by external pressure via a resonant mixing of f- and conduction electrons in the vicinity of the the Fermi surface. It is also found that: 1. An increase of mixing leads to a decrease of the physical values of the Hubbard interactions, $U^*$, the reduction, however, is small. 2. The initial Hubbard U is split by renormalization into a set of different physical values of $U^*_{i,j}$. 3. The gain in cohesive energy together with the f-sum rule cause a transfer of spectral weight, which is decisive for the delocalization of \f-electrons. 4. The correlated Fermionic quasi particles have their bandwidth slightly reduced compared to the ones obtained by means of the Kohn-Sham equation.