Comparison of the superexchange interaction in NiO and in a NiO[100] surface

The superexchange interaction, parameterized by J, of bulk NiO and the NiO[100] surface was investigated using ab initio quantum chemical techniques. J is influenced by two opposing mechanisms; the reduced Madelung potential at the surface leads to a small increase, whereas the change in the nickel coordination from six to five oxygens gives a larger decrease. As a result J at the [100] surface is predicted to decrease by about 20% with respect to the bulk. This contradicts another recent prediction to the effect that J should increase by about 50%. Experimental data are not yet available.