Crystal field and magnetic structure of UO2

The properties of UO2 result from rich f-electron physics, including electronic Coulomb interactions, spin-orbit and crystal-field effects, as well as interionic multipolar coupling. We present a comprehensive theoretical study of the electronic structure of UO2 using a combined application of self-consistent DFT + U calculations and a model Hamiltonian. The Gamma(5) ground state of U4+ and the energies of crystal-field excitations Gamma(5) -> Gamma(3,4,1) are reproduced in very good agreement with experiment. We also investigate competing noncollinear magnetic structures and confirm 3k as the T = 0 K ground-state magnetic structure of UO2.