Long chain-length behaviors of optical nonlinearities of substituted polyenic chains with charged topological defects

The long chain-length behaviors of the static polarizability alpha and second hyperpolarizability gamma of species of polyenic chains with various combinations of donor-acceptor substitutions and charged topological defects are studied by ab initio finite-field method. Both alpha and gamma were found to exhibit linear chain-length dependent growth in the long chain-length limit for all combinations. The growth rates are universal, independent of the presence or absence of the substitutions or the charged topological defects. The origin of the universal growth is discussed using a local-view formalism that is based on the local atomic charge derivatives. It is found that this formalism can provide quantitative accounts of the saturated growth of alpha and gamma. The effects on alpha and gamma of a polyenic chain by the presence of a charged topological soliton are found to be additive. This allows the identification and calculation of the polarizability and second hyperpolarizability of a stand-alone charged soliton. (C) 2001 American Institute of Physics.