Frequency dependent hyperpolarizabilities of polyynes

Abstract

Ab initio calculations have been performed for the static and dynamic polarizability and hyperpolarizability for a series of polyynes C 2nH2 using self-consistent field (SCF) (n=1-6) and multiconfiguration self-consistent field (MCSCF) (n=1-4) wave functions. We have considered the longitudinal component of the static hyperpolarizability and the same component of the dynamic hyperpolarizability measured in electric-field induced second harmonic generation γESHG=γ(- 2ω;ω,ω,0). The frequency dependence of the polarizability and hyperpolarizability has been rationalized in terms of the coefficients in expansions in ω2. The static hyperpolarizabilities vary smoothly with the chain length and satisfy γ(C2nH 2)=γ (C2H2) ×nX, where X≈3.0. The dynamic hyperpolarizability satisfies a similar relation where X increases slowly with ω. © 1993 American Institute of Physics.