A study of iodine-doped transpolyacetylene

With a view to elucidate and develop a model for the mechanism of conduction in doped transpolyacetylene (t-PA) we have carried out an ab initio study of the ground and excited state of transoctatetraene in the presence of an Iodine atom. While the ground state is calculated as characterized by a slightly distorted alternating bond geometry with Iodine remaining largely neutral atop the plane of the polyene near roughly the midpoint of chain axis, the excited state has the geometry characterized by a solitonic distortion with the octatetraene carrying a net positive charge close to .7e. The bandgap (HOMO-LUMO gap) is computed to be nearly .8 eV. Moreover, the excited state energy appears very insensitive to the position of Iodine along the axis of the octatetraene chain. As an extension of an earlier calculation on the transport of charge by a charged soliton, a similar calculation is performed on a C8Hi10+ “kink” travelling along the backbone of C12H14+ yielding very similar results. We have extended the ab initio calculations also to the infinite chain.