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-order hyperpolarizability of polyyne, polyacetylene and polypyrrole oligomers is compared using second-order Møller-Plesset perturbation theory (MP2). In general, the MP2 hyperpolarizability is found to be significantly greater than the Hartree-Fock (HF) estimate. The bulk of the difference is traced to a correlation-induced reduction in the bond length alternation of the polymer backbone. A more efficient electron correlation scaling procedure for hyperpolarizabilities of π-conjugated polymers based on HF values found using the MP2 infinite polymer geometry is proposed.