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Crystal field and magnetic structure of UO$_{2}$

The properties of UO$_{2}$ result from rich $f$-electron physics, including electronic Coulomb interactions, spin-orbit and crystal field effects, as well as inter-ionic multipolar coupling. We present a comprehensive theoretical study of the electronic structure of UO$_{2}$ using a combined application of self-consistent DFT+$U$ calculations and a model Hamiltonian. The $Γ_{5}$ ground state of U$^{4+}$ and the energies of crystal field excitations $Γ_{5} \rightarrow Γ_{3,4,1}$ are reproduced in very good agreement with experiment. We also investigate competing non-collinear magnetic structures and confirm 3-k as the T=0 K ground state magnetic structure of UO$_2$.