Effects of disorder on the electronic structure of undoped polyacetylene

A theoretical investigation of disorder in undoped polyacetylene indicates that a substantial amount of topological and structural disorder is consistent with the experimental work done to date. Certain topological defects (chain ends and cross links) are found to be unstable to soliton emission, with the remarkable consequence that odd-membered finite chains always contain a soliton. Relaxations of the stable defects are determined. Various kinds of structural disorder are studied; these include admixtures of cis-isomerization, bending and twisting of chains, local interchain interactions, and stochastic bond-length fluctuations. The effect upon the electronic density of states is calculated in each case. When some chain bending is included, that a distribution of interchain interaction and a plausible amount of bond-length disorder may explain the observed broadening of the Peierls edges.