Key points are not available for this paper at this time.
The methods of previous papers by the authors are applied to a simplified impurity calculation. This is the case of a localized perturbation in a simple cubic lattice. We consider the effect of the perturbation on a single band which is describable in terms of a Wannier function which only has nearest neighbor interactions. The results of this calculation are compared with some approximate treatments of impurity calculations.
Koster et al. (Wed,) studied this question.