  We report calculations of the electronic structure of FeO in the LDA and
LDA+U approximation with and without rhombohedral distortion. In both cases LDA
renders an antiferromagnetic metal, and LDA+U opens a Hubbard gap. However, the
character of the gap is qualitatively different in the two structure, and the
difference can be traced down to underlying LDA band structure. An analysis of
the calculations gives a new insight on the origin of the insulating gap in 3d
monoxides and on the role of the k-dependency of U, missing in the contemporary
LDA+U method.
