Delocalization Contributions to Polyacetylene Force Fields

Abstract The force fields of trans and cis-polyacetylene(PA) are obtained in internal coordinates by combining linear-response analysis of the Raman and ir shifts due to π-electrons, molecular force-field methods, and the Huckel susceptibility of k ≠ 0 phonons. We find transferable electron-phonon coupling constants, exponential transfer integrals t(R), and coupling to CCC bends through the Coulomb potential V(R). The electronic response of cis-PA is 56% of the trans susceptibility, indicative of reduced delocalization and an energy gap in the Ag manifold due to third-neighbor V(R) terms.

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