Ab-initio study on the inter-molecular interactions in polythiophene

We report the fully three-dimensional band structure of polythiophene (PT) calculated within density functional theory (DFT) using the full-potential linearized augmented plane wave method. Two different arrangements of the polymer chains are considered as found in the low and high temperature polymorphs, respectively, of the 4- and 6-unit oligomers of PT. We analyze the band dispersions perpendicular to the polymer direction and the band splittings resulting from the overlap of wave functions on neighboring molecules. We find an energetic splitting of only 0.1 eV for the HOMO wave functions of the low temperature structure as compared to 0.4 eV for the high temperature modification suggesting a much higher carrier mobility for the latter.