9. NiO: DOS for different magnetic states

Above is the same density of states for a HF solution of ferromagnetic NiO. You can see it hardly differs at all from the antiferromagnetic solution (repeated for comparison). You may recall what I said earlier about Slater's alternative theory of magnetic insulators which involved doubling the unit cell due to the antiferromagnetic lattice opening a band gap at the new zone boundaries. In fact the energy scale of the magnetic interaction is orders of magnitude smaller than that of the on-site Coulomb interactions, and is much too small for this to have any direct effect on the insulating behaviour.

Now I can use these kinds of calculations to estimate superexchange coupling constants, but for the moment this is irrelevant (see later). For the moment we're just interested in the gross electronic structure.