Band structure studies of actinide systems

The nature of the f-orbitals in an actinide system plays a crucial role in determining the electronic properties. It has long been realized that when the actinide separation is small enough for the f-orbitals to interact directly, the system will exhibit itinerant electron properties: an absence of local moment due to the f-orbitals and sometimes even superconductivity. However, a number of systems with the larger actinide separation that should imply local moment behavior also exhibit itinerant properties. We have been examining such systems (URh3, UIr3, UGe3, UC) to learn something about the other f-interactions. A preliminary observation we have made is that there is apparently a very large and anisotropic mass enhancement in these systems. There is very good reason to believe that this is not solely due to large electron-electron correlations but to a large electron-phonon interaction as well. These features of the ''non-magnetic'', large actinide separation systems will be discussed in light of our results to date. Finally, the results of some recent molecular calculations on actinide hexafluorides will be used to illustrate the shielding effects on the intra-atomic Coulomb term Usub(f-f) which would appear in any attempt to study the formation of local moments. As one becomes interested in materials for which a band structure is no longer an adequate model, this screened Usub(ff) is the significant parameter and efforts must be made to evaluate it in solid state systems. (author)