Coupled-perturbed Hartree-Fock treatment of infinite periodic systems: Application to static polarizabilities and hyperpolarizabilities of polydiacetylene, polybutatriene, and interacting pairs of polyacetylene chains

Static longitudinal polarizabilities (α) and second hyperpolarizabilities (γ) are determined for three quasi-one-dimensional polymeric systems using a new crystal orbital coupled-perturbed Hartree-Fock method. Calculations of α and γ for polydiacetylene and polybutatriene at two different geometries are analyzed in terms of the alternation of bond lengths along the carbon backbone. For the third polymer, polyacetylene, the treatment is applied to a pair of chains in the two different configurations that occur in a stretched fiber. The results are in marked contrast to those previously obtained for short and medium-sized oligomers. In order to relate the pair interaction effect between infinite chains to the bulk susceptibility of the natural fiber additional finite oligomer calculations are carried out. This allows us to discuss the role of finite chain length distribution, many-body interchain interactions, and electron correlation.