As many semiconducting polymers such as P(NDI2OD-T2) have a relatively rigid backbone and extended conjugation, their bonded parameters -particular between conjugated units -and charges are not expected to be accurately captured by general-purpose molecular-dynamics force fields. To accurately model these systems, certain parameters must therefore be determined for the specific molecules of interest. Here we have based our parameterisation on the OPLS force field, as it has been shown to accurately describe structural and thermodynamic properties of several small-molecule OSCs 66,67 and many organic liquids, which are commonly used as solvents for OSCs. We note that a previous AA model of P(NDI2OD-T2) has been parameterised with the AMBER force field, but, to the best of our knowledge, no OPLS parameters exist for this polymer.