Relativistic many-body effects in the fine and hyperfine structure of i139 (5d+6s)2 J=2 states: The need for second-order electrostatic corrections

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Using our relativistic-configuration-interaction methodology, we report multireference calculations of energy differences and magnetic-dipole and electric-quadrupole hyperfine structure constants of all five levels in the (5d+6s)2 J=2 manifold of singly ionized La139. The errors in the splittings of the bottom four levels are no more than 0.02 eV, while the separation of the two highest levels has an error of 0.11 eV due to an incomplete description of the correlation in the levels belonging to higher manifolds. The hyperfine-structure constants show strong sensitivity to many-body effects, resulting in striking improvements over the multiconfiguration Dirac-Fock values. Seven of the ten hyperfine constants are accurate within 2-12 %. For the rest of the constants we have identified the primary cause of the errors as an incorrect description of many-body effects in the high-lying levels and have discussed possible remedies. © 1995 The American Physical Society.

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Physical Review A