Magnetic structure and electric-field gradients of uranium dioxide: Anab initiostudy

The magnetic structure of uranium dioxide has been investigated using linear augmented plane wave ab initio calculations, taking into account spin-orbit coupling, strong Coulomb correlation (using the LDA+U approach) and noncollinear magnetism. The collinear 1-k antiferromagnetic type-I structure and the noncollinear antiferromagnetic 2-k and 3-k orderings have been tested. The 1-k and 2-k structures can be excluded by a comparison between the calculated and experimental uranium electric field gradients (EFG). It is shown that the measured EFG agrees with theory only in the 3-k structure and an additional deformation of the oxygen cage with an oxygen displacement of ΔO=0.16a.u. Also the magnetic moments and the corresponding hyperfine fields agree reasonably well with experiment.