Abstract
Techniques are given for representing a periodic function of cubic symmetry in terms of a sum over a finite set of orthogonal functions. General results for cubic lattices are tabulated in a form convenient for use in computation. The accuracy of an approximation may be improved systematically by augmenting an approximate set of points. The special points of Chadi and Cohen occur as a case in which the periodic function is evaluated at a sublattice of points. Other sublattices may also be used. Such sets of points are found to be in the spirit of the original Baldereschi special points because certain orthogonal functions in the expansion are identically zero for all sublattice points.