Double harmonic vibrational second hyperpolarizabilities of polyyne chains

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The RHF/6-31G longitudinal vibrational second hyperpolarizabilities of increasingly longer polyyne chains have been computed within the double harmonic oscillator approximation. Similarly to polyacetylene, the largest contribution comes from the [α2]0,0 term. About 95% of the latter arises from what we call the quasi-ECC mode. It converges rapidly with chain length to an asymptotic limit slightly (7%) smaller than its static electronic counterpart. The [μβ]0,0 term is negligible. The inclusion of electron correlation within the MP2/6-31G scheme leads to a decrease of the γve ratio by a factor going from roughly 3 for the dimer to 2 for the tetramer.

Original languageEnglish
Pages (from-to)115-122
Number of pages8
JournalJournal of Molecular Structure: THEOCHEM
Issue number1-2
Publication statusPublished - 19 Feb 1998


  • Ab initio quantum chemical calculations
  • Electronic second hyperpolarizability
  • Polyyne chains
  • Vibrational second hyperpolarizability


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