Ab initiocalculation of 4fN6s2hyperfine structure in neutral rare-earth atoms

The multiconfiguration Dirac-Fock (MCDF) method is used to calculate excitation energies, Landé g values, and hyperfine-structure (hfs) constants for the lowest multiplets of the 4$f^N$6$s^2$ configurations of neutral rare-earth atoms. Although no adjustable parameters are used, the results are in rather good agreement with experiment. The calculated excitation energies and dipole hfs constants (using the known moment values) differ from experiment by typically 5%, and the g values by 0.1%. Relative to quadrupole moment values determined from muonic-atom hfs or Coulomb excitation, the calculated electric-quadrupole hfs is typically (30±2)% too large, consistent with a Sternheimer shielding factor (not included in the MCDF calculations) of $R_{4f}$=+0.23. The calculated J dependence for all four observables is generally in good agreement with experiment for the ground multiplets. Particular cases where the MCDF results are less accurate are identified and discussed.