Gl. Bendazzoli et S. Evangelisti, THE PPP MODEL OF ALTERNANT CYCLIC POLYENES WITH MODIFIED BOUNDARY-CONDITIONS, International journal of quantum chemistry, 55(4), 1995, pp. 347-359
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 bou
ndary conditions. Full CI computations are carried out for some low-ly
ing states of the PPP model of alternant cyclic polyenes (CH)(N) (N ev
en) at half-filling. The energy values obtained by using periodic (Blo
ch) and antiperiodic (Mobius) orbitals are used to perform energy extr
apolations for N --> infinity. (C) 1995 John Wiley and Sons, Inc.