A COMPARATIVE-STUDY OF THE EFFECT OF ELECTRON CORRELATION IN THE HYPERPOLARIZABILITY OF POLYYNE, POLYACETYLENE AND POLYPYRROLE OLIGOMERS

The effect of electron correlation on the static longitudinal second-o rder hyperpolarizability of polyyne, polyacetylene and polypyrrole oli gomers is compared using second-order Moller-Plesset perturbation theo ry (MP2). In general, the MP2 hyperpolarizability is found to be signi ficantly greater than the Hartree-Fock (HF) estimate. The bulk of the difference is traced to a correlation-induced reduction in the bond le ngth alternation of the polymer backbone. A more efficient electron co rrelation scaling procedure for hyperpolarizabilities of pi-conjugated polymers based on HF values found using the MP2 infinite polymer geom etry is proposed.