Multiconfigurational quasidegenerate perturbation theory

The second theoretical calculation is by Tatewaki et al. [22] They used four-component relativistic multiconfigurational quasidegenerate perturbation theory to take account of correlation effects between the active core [Ce + 4s. ..5p )F (2s 2p )] and three valence electrons in (4/), (5d), (6s), (6p), and intra-valence correlation effects. For the energy levels of the two excited states they obtained 0.144 eV and 0.351 eV. They did not reach conclusions about the higher excited states because of the limitations of the theory they used. A further study of the CeF excited states using larger RASCI and the/-shell Omega decomposition method (which is described below) is under way. 

H. Moriyama, Y. Watanabe, H. Nakano, and H. Tatewaki, Electronic structure of LaF+ and LaF from frozen-core four-component relativistic multiconfigurational quasidegenerate perturbation Theory, J. Phys. Chem. A112, 2683-2692 (2008). 

Nakano H (1993) Quasidegenerate perturbation theory with multiconfigurational self-consistent-field reference functions. J Chem Phys 99 7983... 

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