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It is demonstrated explicitly that diagonalization of the 4d 9 nf channel in neutral atomic Ba (Ba I) leads to a 4d 9 4f 1 P resonance below the 4d 9 -ionization threshold in complete agreement with a direct Hartree-Fock calculation for the 4d 9 4f 1 P level. The wavefunction for the 4d 9 4f 1 P level is energetically and spacially very close to the 4d 9 5f level from average-of-configuration Hartree-Fock.
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Göran Wendin (1976) studied this question.
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