AB-INITIO LCAO HARTREE-FOCK MOLECULAR-ORB ITAL STUDY ON THE CUBIC HYPERPOLARIZABILITY OF CONJUGATED OLIGOMERS

Ab-initio LCAO CPHF (Coupled perturbed Hatree-Fock) study was performe d to calculate the longitudinal cubic hyperpolarizability of the polya cetylene and polydiacetylene oligomers. The theoretical calculation su ccessfully reproduced the experimentally measured non-resonant THG val ues of the hyperpolarizabilities of the polyacetylene oligomers. The e ffect of the conjugation pattern on the hyperpolarizability was invest igated. The hyperpolarizability of the polyacetylene oligomers was fou nd to be larger than that of the polydiacetylene ones. We could estima te the order of the nonlinearity of corresponding polymer systems from the results of oligomer calculations. These reconfirmed the spatial l ocality of the process in the nonlinear optical phenomena.