  Increasing experimental and theoretical evidence points towards a dual nature
of the 5$f$ electrons in actinide-based strongly correlated metallic compounds,
with some 5$f$ electrons being localized and others delocalized. In a recent
paper (PRB xxx, 2004), we suggested the interplay of intra-atomic correlations
as described by Hund's rules and a weakly anisotropic hopping (hybridization)
as a possible mechanism. The purpose of the present work is to provide a first
step towards a microscopic description of partial localization in solids by
analyzing how well various approximation schemes perform when applied to small
clusters. It is found that many aspects of partial localization are described
appropriately both by a variational wavefunction of Gutzwiller type and by a
treatment which keeps only those interactions which are present in LDA+U
calculations. In contrast, the energies and phase diagram calculated within the
Hartree Fock approximation show little resemblence with the exact results.
Enhancement of hopping anisotropy by Hund's rule correlations are found in all
approximations.
