The approximate calculation of electronic band structure

An approximate representation of the phase shifts of atomic potentials is derived making use of the weakness of the pseudopotential. By using this representation in conjunction with the Korringa-Kohn-Rostoker scheme for band structure calculation, various approximate schemes for band structure calculation are derived. In particular, when no virtual resonances are present one obtains the well-known pseudopotential method, and when a single virtual resonance is present one obtains a hybrid tight-binding plane wave scheme of the kind recently discussed by Heine and others.