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 p olymer chains are considered as found in the low and high temperature polym orphs, respectively, of the 4- and 6-unit oligomers of PT. We analyze the b and dispersions perpendicular to the polymer direction and the band splitti ngs 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 o f the low temperature structure as compared to 0.4 eV for the high temperat ure modification suggesting a much higher carrier mobility for the latter.