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Energy-band calculations have been performed for Ce, Pr, and Nd. The normal local-spin-density approximation to exchange and correlation for the potential is used but spin-orbit coupling and a newly developed additional contribution to the 4f eigenvalue splittings arising from orbital polarization of the 4f electrons are also included. This procedure represents the application of all three Hund's rules in the solid state. The observed volume collapses of the light rare-earth metals are correctly described by theory.
Eriksson et al. (Sun,) studied this question.