A STUDY OF IODINE-DOPED TRANSPOLYACETYLENE

With a view to elucidate and develop a model for the mechanism of cond uction in doped transpolyacetylene (t-PA) we have carried out an nb in itio study of the ground and excited state of transoctatetraene in the presence of an Iodine atom. While the ground state is calculated as c haracterized by a slightly distorted alternating bond geometry with Io dine remaining largely neutral atop the plane of the polyene near roug hly the midpoint of chain axis, the excited state has the geometry cha racterized by a solitonic distortion with the octatetraene carrying a net positive charge close to .7e. The bandgap (HOMO-LUMO gap) is compu ted to be nearly .8 eV. Moreover, the excited state energy appears ver y insensitive to the position of Iodine along the axis of the octatetr aene chain. As an extension of an earlier calculation on the transport of charge by a charged soliton, a similar calculation is performed on a C8H10+ ''kink'' travelling along the backbone of C12H14+ yielding v ery similar results. We have extended the ab initio calculations also to the infinite chain.