SIMULTANEOUS PRESENCE OF 2 CHARGES OR 2 SPINS IN A LINEAR POLYENE - MULTIELECTRON POPULATIONS IN OCTATETRAENE FROM A PPP-TOTAL) CI WAVE-FUNCTION((QUASI)

In this work we examine the ease of finding simultaneously two charges or two spins in various AO positions of a linear neutral polyene such as octatetraene. By applying the general multi-electron population an alysis on a correlated wave function we calculate contributions from v arious ionic and covalent (in a probabilistic sense) resonance structu res as well as electron-pair distributions with parallel and anti-para llel spins; the initial wave function used is a PPP + (quasi-total) CI wave function. Based on the second and fourth order anticommutation r elations (and independently of the level of the MO wave function used) we show existing relationships between the quantities considered, as well as their constant behaviour. Covalent structures depend strongly on the parity and distance between the AO positions, while ionic ones are quasi-constant along the polyene. It is also shown that when the A O positions considered are non-vicinal, (+) and (-) charges appear mut ually independent and the pi-electron conjugation has, rather surprisi ngly, no effect on them.