Electron correlation and relativity of the 5f electrons in the U–Zr alloy system

We address a recently communicated conception that spin–orbit interaction and strong electron correlations are important for the metal fuel U–Zr system. Here, we show that (i) relativistic effects only marginally correct the uranium metal equation-of-state and (ii) addition of onsite Coulomb repulsion leads to an unphysical magnetic ground state of the body-centered cubic (γ) phase and a grossly overestimated equilibrium volume. Consequently, LSDA + U is deemed unsuitable for describing the electronic structure of the U–Zr system.