Theoretical study of relativistic effects in the electronic structure of Pu

We present a theoretical study of atomic and fcc Pu related to the treatment of relativistic effects and equilibrium fcc volume. The unusually large error in the theoretical fcc volume has been recognized as a fundamental problem of metal physics. The commonly employed second variational treatment of the spin-orbit splitting in Pu is found to have a large $(\simeq 25\%)$ error in dealing with the $6p$ semicore states but not the $5f$ states of the Pu atom. In fcc Pu, this error implies a corresponding nontrivial effect on various calculated equilibrium properties including the lattice volume. This points to the importance of correctly treating the localization of the $6p$ as well as the $5f$ electronic states in fcc Pu and thereby recognizing the importance of specific relativistic effects for the $6p$ electrons that appear to have been ignored up to now.