The cellular method for non-spherical potentials

Abstract
A form of the cellular method is developed in which the non-spherical terms in the potential can be treated exactly. Examples of its use are given for copper metal and graphite crystal. In the latter, eigenvalues change in most cases by 0.2-0.3 Ryd as a result of introduction of the non-spherical potential and it is also found that layer-layer interaction cannot be considered small.