Density-functional-based tight-binding approach to polarons in conjugated polymers

Whether or not charge injection leads to polaron formation in conjugated polymers remains a matter of controversy with profound qualitative discrepancies between different methods. In this paper we show that the Density-functional-based tight-binding (DFTB) approach of Porezag et al. predicts delocalization of an excess charge and thus no polaron formation in infinite conjugated polymer chains. Since real polymers have finite conjugation lengths, we also present the first comparative study of electron and hole polaron binding energies in oligomers of the conjugated polymers trans-polyacetylene (tPA), poly(para-phenylene) (PPP) and poly(para-phenylene vinylene) (PPV).