  The crystal field splitting and d bandwidth of the 3d transition metal
monoxides MnO, FeO, CoO and NiO are analyzed as a function of pressure within
density functional theory. In all four cases the 3d bandwidth is significantly
larger than the crystal field splitting over a wide range of compressions. The
bandwidth actually increases more as pressure is increased than the crystal
field splitting. Therefore the role of increasing bandwidth must be considered
in any explanation of a possible spin collapse that these materials may exhibit
under pressure.
