Semiclassical method for calculating quantum-lattice-fluctuation effects in conducting and/or optically active polymers, with results for polyacetylene in the soliton-antisoliton approximation

Deviations from the lowest-energy configuration due to the quantum nature of the lattice–called quantum lattice fluctuations (QLF’s)–may significantly affect the properties of conjugated polymers. In this paper, we present a semiclassical method for including QLF effects in calculations of conducting and/or optically active polymer properties. We then apply the method to the first- and third-order absorption intensities of pristine finite chains of trans- and cis-(CH)_x containing fluctuation-induced soliton-antisoliton pairs. The first-order results agree with previous calculations, which used different methods. Third-order results indicate that QLF effects are enhanced by asymmetry, and degraded by disorder. They are most important below the three-photon peak, and remain substantial even for nondegenerate ground-state polymers.