THE PPP MODEL OF ALTERNANT CYCLIC POLYENES WITH MODIFIED BOUNDARY CONDITIONS

摘要

The extension of the PPP Hamiltonian for alternant cyclic polyenes to noninteger values of the pseudomomentum by imposing modified boundary conditions is discussed in detail. It is shown that a computer program for periodic boundary conditions can be easily adapted to the new boundary conditions. Full CI computations are carried out for some low-lying states of the PPP model of alternant cyclic polyenes (CH)(N) (N even) at half-filling. The energy values obtained by using periodic (Bloch) and antiperiodic (Mobius) orbitals are used to perform energy extrapolations for N --> infinity. (C) 1995 John Wiley and Sons, Inc. [References: 46]