Effect of solid-state interactions on the vibrational hyperpolarizability of all-trans polyacetylene chains from ab initio Hartree-Fock calculations

Coupled perturbed Hartree-Fock/6-31G finite oligomer cluster calculations are carried out, which show that solid-state interactions lead to a large decrease in the vibrational hyperpolarizability of all-trans polyacetylene. The vibrational property behaves similarly to the corresponding electronic property with increasing cluster size. Low-frequency collective and interchain modes are very significant for small oligomers, but the high-frequency vibrations that are most important for a single chain become dominant as the chains are lengthened. Since the solid-state interactions do not modify the geometry of the individual chains the decrease of the vibrational and electronic hyperpolarizabilities in polyacetylene is due to direct electronic effects. (C) 1998 American Institute of Physics. [S0021-9606(98)70139-4].