, Volume 74, Issue 6, pp 479-491

The atomic states of nickel

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Abstract

The Ni 3d 9 4s 1(3 D)−3d 10(1 S) and 3d 9 4s 1(3 D)-3d 84s 2(3 F) atomic excitation energies have been computed using large multireference CI wave functions in conjunction with a large ANO basis set. Radial correlation effects in the 3d shell are found to be very important and are included using CASSCF wave functions having the 3d and correlating 3d′ orbitals in the active space. The previous discrepancy (0.5 eV) with experiment for the 3 D1 S excitation is reduced to 0.1 eV when the 3d→3d′ references are included in the CI. For the 3 F state, the 4s-4p near degeneracy gives rise to important 4s 2→4p 2 excitations in addition to the 3d→3d′ excitations which are important for the 3 D and 1 S states. Inclusion of only 3d-3d′ correlation in the 3 F and 3 D CI reference spaces yields a 3 F3 D separation which is in error by 0.12 eV. Addition of the 4s 2→4p 2 excitations to the 3 F reference space is estimated to increase the discrepancy with experiment by an additional 0.1 eV.