Magnetic state and electronic structure of the δ and α phases of metallic Pu and its compounds -: art. no. 024458

By the local density approximation with on-site Coulomb repulsion U (LDA+U) method with spin-orbit coupling (LDA+U+SO) the magnetic state and electronic structure have been investigated for plutonium in delta and alpha phases and for the Pu compounds PuN, PuCoGa5, PuRh2, PuSi2, PuTe, and PuSb. In agreement with experiment we found for metallic plutonium in both phases a nonmagnetic ground state with Pu ions in f(6) configuration with zero values of spin, orbital, and total moments. This result is determined by a strong spin-orbit coupling in the 5f shell. It leads to the clear splitting of 5f states into f(5/2) and f(7/2) subbands even in the LDA calculation. The Fermi level is in a pseudogap between them, so that the f(5/2) subshell is already almost completely filled with six electrons before Coulomb correlation effects are taken into account. The competition between spin-orbit coupling and the exchange (Hund) interaction (favoring a magnetic ground state) in the 5f shell is so delicately balanced that a small increase (less than 15%) of the exchange interaction parameter value from J(H)=0.48 eV obtained in the constrained LDA calculation would result in a magnetic ground state with nonzero spin and orbital moment values. For the Pu compounds investigated in the present work, a predominantly f(6) configuration with nonzero magnetic moments was found in PuCoGa5, PuSi2, and PuTe, while PuN, PuRh2, and PuSb have the f(5) configuration with sizable magnetic moment values. Whereas the pure jj coupling scheme was found to be valid for metallic plutonium, an intermediate coupling scheme is needed to describe the 5f shell in Pu compounds. The results of our calculations show that the exchange interaction term in the Hamiltonian should be treated in a general matrix form for Pu and its compounds.