Unrestricted Hartree—Fock Calculations on Linear-Atomic-Chain Models Yielding the ``Surface'' (End) States

Restricted and unrestricted Hartree—Fock methods have been applied to the study of the properties of the Tamm and Shockley surface states. Linear polyenic chains were chosen as models and the PPP-type semi-empirical method used. The SPO (spin-polarized orbital) results on Tamm surface states and their physical interpretations are discussed. Further, the radical—or polyradical—character of atomic chains yielding the Shockley surface states was obtained and is discussed. Possible implications for the surfaces of real semiconductor crystals and their geometry are suggested.