THE PI-ELECTRONS OF POLYTHIOPHENE

A first-principles method is applied on different structures of polythiophene ranging from quinoid to aromatic. Special emphasis is put on the pi-bands as functions of structure. Based on the findings we propose a pi-electron tight-binding model, which is used in studying solitons and polarons. The results show that sulphur-centered functions are important, that solitons do not induce near-mid-gap states, that polarons give states asymmetric in the gap, and that bipolarons and not polarons are created in doped or photoexcited chains.