CHAIN-LENGTH DEPENDENCE OF STATIC LONGITUDINAL POLARIZABILITIES AND HYPERPOLARIZABILITIES IN LINEAR POLYYNES

Ab initio calculations of the static longitudinal dipole polarizabilit y alpha(L) and second dipole hyperpolarizability gamma(L) are reported for the linear C2nH2 polyynes up to C44H2. Basis set requirements dim inish with increasing chain length. The intermediate neglect of differ ential overlap (INDO) method is able to mimic the ab initio results if the Ohno-Klopman parameterization is used. The values per acetylenic linkage, alpha(L)/n and gamma(L)/n, converge very slowly with chain le ngth; they are extrapolated to the infinite chain limit.