SEMIEMPIRICAL DETERMINATION OF DYSONS STATES IN CONJUGATED SYSTEMS WITHIN A FULL-CI PI-ELECTRON SCHEME

The Dyson states as orbitals and geminals describing one- and two-elec tron detachment processes in molecules are treated within a spin-free formulation of the full configuration interaction (CI) theory. The ens uing computational scheme is presented and some semiempirical calculat ions on pi-shells are given for unsaturated hydrocarbons such as mediu m-sized polyenes and aromatics. It is shown that in these systems the correlation effects turn out to be more important than the relaxation effects, leading to a marked reduction in the calculated full-CI photo ionization cross-sections relative to the Hartree-Fock ones.