2ND HYPERPOLARIZABILITY OF HUCKEL RINGS - ANALYTICAL RESULTS FOR SIZE AND ALTERNATION DEPENDENCIES

We analyze the size and alternation dependence of the second static hyperpolarizability gamma(0;delta,N) of N-site Huckel rings with transfer integrals t(1+/-delta). Regular (delta = 0) rings lead to a simple gamma(0;0,N) is similar to N5 dependence, while alternating (delta > 0) chains show a delta-6 divergence in the band limit. Analytical results for noninteracting electrons clarify the evolution from molecules to polymers, show strong enhancement of gamma(0;delta,N) in the region Ndelta almost-equal-to 1, and connect previous oligomer and polymer calculations.