1. New Method for Calculating Wave Functions in Crystals and Molecules
2. M. L. Cohen and V. Heine, this volume (referred to as CH).
3. V. Heine and D. Weaire, this volume (referred to as HW).
4. J. M. Ziman,Solid State Phys. (to be published).
5. Atomic units (s.u.) withm = h = e = 1 will be used throughout, the unit of length being the first Bohr radius and the unit of energy the double rydberg = 27.2 eV.