The atomic states of nickel
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- Bauschlicher, C.W., Siegbahn, P. & Pettersson, L.G.M. Theoret. Chim. Acta (1988) 74: 479. doi:10.1007/BF00528018
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The Ni 3d9 4s1(3D)−3d10(1S) and 3d9 4s1(3D)-3d84s2(3F) 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 3D−1S excitation is reduced to 0.1 eV when the 3d→3d′ references are included in the CI. For the 3F state, the 4s-4p near degeneracy gives rise to important 4s2→4p2 excitations in addition to the 3d→3d′ excitations which are important for the 3D and 1S states. Inclusion of only 3d-3d′ correlation in the 3F and 3D CI reference spaces yields a 3F−3D separation which is in error by 0.12 eV. Addition of the 4s2→4p2 excitations to the 3F reference space is estimated to increase the discrepancy with experiment by an additional 0.1 eV.