Theoretical study of relativistic effects in the electronic structure of Pu

We present a theoretical study of atomic and fee Pu related to the treatmen t of relativistic effects and equilibrium fee volume. The unusually large e rror in the theoretical fee volume has been recognized as a fundamental pro blem of metal physics. The commonly employed second variational treatment o f the spin-orbit splitting in Pu is found to have a large (similar or equal to 25%) error in dealing with the 6p semicore states but not the 5f states of the Pu atom. In fee Pu, this error implies a corresponding nontrivial e ffect on various calculated equilibrium properties including the lattice vo lume. This points to the importance of correctly treating the localization of the 6p as well as the 5f electronic states in fee Pu and thereby recogni zing the importance of specific relativistic effects for the 6p electrons t hat appear to have been ignored up to now.