ELECTRONIC-STRUCTURE OF HEAVILY DOPED POLYACETYLENE

We present results of first-principles, density-functional calculations on isolated trans-polyacetylene chains doped periodically at 100% and 33% concentration with Li, Be, B, C, N, O, F, Ne, or Na atoms as well as results for undoped chains. We focus on the electronic orbitals and have not attempted to optimize the structures. The results indicate the presence of non-negligible interactions between the orbitals of the dopants and those of the polymer, as seen, e.g., in a broadening of the energy ranges spanned by the dopant orbitals and in a fractional electron transfer between dopants and polymer. Although the calculations suffer from various approximations, these results-observed for all the dopants-allow us to make more general conclusions about the nature of polyacetylene when doped at lower concentrations and/or with other dopants. It is thus suggested that the experimentally observed doping-induced increase in electrical conductivity also is due to interchain interactions mediated through the dopants, in agreement with the experimental results of Bernier and co-workers. Finally, as a by-product our results demonstrate inaccuracies in electron transfers when studying weakly interacting systems using local-density calculations.