  The band structure of a strongly correlated semiconductor as NiO has been the
object of much debate [PRL 103, 036404 (2009); PRL 102, 226401 (2009)]. Most
authors, using computational techniques well beyond the simple density
functional theory and the approximations GGA or LDA, claim that the band gap is
about 4.0 eV and that the conduction band is of Ni-3d nature. Thus they seem to
forget the results of electron energy-loss spectroscopy and inelastic x-ray
scattering, both able to determine electronic transitions of only about 1.0 eV
to an optically forbidden Ni-3d band. Further, a simple atomic calculation of
the Ni++ spin flip energy demonstrates that a Ni-3d band at 4.0 eV is
impossible. To set the issue straight, we calculated NiO with the very
successful technique of PRB 78, 125116 (2008). It turns out that a band at 4.0
eV is optically accessible and made of excited atomic states, not Ni-3d. Aside
from that, we also found a narrow Ni-3d band at about 1.0 eV. To confirm our
procedures once again, we also calculated MnO and obtained the standard results
of the good calculations as those cited above, and of experiment.
