Phenomenological theory of soliton formation in lightly-doped polyacetylene

A phenomenological theory is introduced to investigate the influence on soliton formation of the Coulomb repulsion associated with the double occupation of the soliton's localized mid-gap state and the soliton's interaction with the iodized dopant molecule. Markedly different equilibrium parameters result for the neutral, charged-free and charged-pinned soliton forms. The frequency of the i.r. active pinning mode is predicted to be of the order of 300 cm^-1. A large zero-point motion is found for shape deformations of the soliton.