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For pt. I see abstr. A25410 of 1971. The usefulness of a 'model building' approach to rare earth configuration interaction is emphasized as an alternative to doing full ab initio calculations. Second order perturbation theory is used to calculate the eleven parameters which characterize the effective two-electron magnetic interaction in both Pr 2+ and Pr 3+ . Good agreement is obtained with the Pr 2+ experimental parameters without introducing screening.
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Copland et al. (1971) studied this question.
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