SYNTHESIS OF BAND AND MODEL HAMILTONIAN THEORY FOR STRONGLY HYBRIDIZING URANIUM SYSTEMS

For a specified chemical environment (e.g., isostructural compound), uranium typically shows the most delocalized correlated f-electron behavior of the light rare earths and actinides. This provides perhaps the most interesting correlated f-electron behavior for phenomena such as heavy fermion behavior, but also provides the greatest difficulty for the theory. Here we are concerned with the synthesis of band and model(Anderson lattice) Hamiltonian theory to be able to evaluate the phenomenological behavior on a materially predictive ab initio basis. In previous studies for cerium and plutonium systems, use was made of U(the correlation energy) being rather large in dealing with the f-f banding term, derived from the Schrieffer-Wolff transformation of the Anderson lattice Hamiltonian. Since the bandwidth is suppressed by a factor of 1/U, it was justified to neglect the f-f banding term. This is not justified for uranium systems which have a much smaller U. Therefore, rather than treating f electrons as core(resonant) states during the self-consistent band calculation, we first treat 5f's as valence electrons and determine the self-consistent potential. Then the density of states, and hence the f bandwidth (Γ1) which characterizes hybridization between all the band electrons, can be calculated. Then we let the 5f's form bands among themselves, while suppressing hybridization with other bands during the determination of the self-consistent potential. We then use that potential as the basis to calculate the density of states and the f bandwidth (Γ2), which characterizes the hybridization between f's. We then use the value of (Γ1- Γ2), the hybridization strength so obtained, to absolutely evaluate the magnetic ordering behavior and compare with experiment.