Coulomb termUand5felectron excitation energies for the metals actinium to berkelium

Abstract

Relativistic Hartree-Fock-Wigner-Seitz band calculations have been performed for the actinide metals Ac through Bk in order to estimate the Coulomb term $U$ and $5f$ electron excitation energies. Our calculations predict that the tetravalent state (four $6d$-$7s$ conduction electrons) is stable relative to the trivalent state for the lighter elements and that near uranium relative stabilization of the trivalent state occurs. We find that $U$ increases from 2-3 eV for Th to 4-5 eV for the heavier elements considered. $5f$ level widths $W$ are estimated and found to decrease from 2 to 1/2 eV; together with the results for $U$ this points to progressive localization of the $5f$ states. The ratio $\frac{U}{W}$, which is most indicative of localization, takes on values intermediate between those for $3d$ and $4f$ electrons.