Self-Interaction Free Relativistic Local Spin Density Approximation: Equivalent of Hund's Rules inγ-Ce

In this Letter we present an ab initio, density functional theory, justification for the validity of Hund's type of rules in the solid state with localized electrons. We demonstrate that an orbital dependent functional, such as the self-interaction-corrected local spin density, is capable of fully describing the localized nature of the $f$ state, so that all three Hund's rules are fulfilled. We argue this on the basis of linear-muffin-tin-orbital calculations in the atomic-sphere approximation for the $\gamma$ phase of Ce.