Convergence of non-linear optical calculations for infinite polymers -: Second hyperpolarizabilities of polymers with cyclic π-conjugated elementary cells

We have selected several polymers with small elementary cells, poly-HF, poly-H2O, poly-C2H2 and poly-CNH in order to study the convergence of static and dynamic (hyper) polarizabilities at the Coupled Perturbed Hartree-Fock crystal orbital (CO) level. The parameters determining the convergence are the number of k-points over the half Brillouin zone, the number of neighbouring cells treated exactly with the complete Hamiltonian, and the effect of long-range Coulomb interactions. We also present for the first time calculations of the static and dynamic second hyperpolarizabilities gamma on polymers with middle-sized cells, the five-membered heterocyclic pi-conjugated systems, at this level of theory taking into account the results of the convergence study. (c) 2006 Elsevier B.V. All rights reserved.