The OSC studied in this work is a bithiophenethienothiophene copolymer p(g 4 2T-TT) for which double doping was recently demonstrated experimentally. To reduce the computational cost, the tetraethylene glycol side chains are replaced by methoxy groups (Figure ). In the present study the OSC is described by a finite length oligomer consisting of three repeat units. In this first theoretical study on molecular double doping we use the strong CN6-CP p-type dopant. Geometry optimization and calculation of the electronic ground state are based on density funtional theory (DFT) as implemented in the Gaussian 09 program suite . To allow for flexibility in the electronic processes that may occur in the OSC-dopant complexes, we use broken symmetry (BS) DFT calculations, where the α and β orbitals are treated separately, following our and other researchers' previous studies. It should be noted there the α and β channel can actually have mixed spin components in the BS-DFT calculations. The range separated ωB97X-D functional that also includes the dispersion correction (van-der Waals interaction) is used throughout this work along with the 6-31G* basis set. In our previous work, it was shown that the ωB97X-D functional gives a similar description of charge transfer processes as the CAM-B3LYP functional. To account for the effects of neighbouring molecules in an actual OSC environment, a dielectric background of ε = 3 is used within the polarizable continuum model. We note that we did not observe double doping with ε = 2 or smaller values in the calculations. The charge analysis and the projected density of states (PDOS) calculations are performed using the software Multiwfn.