One cannot assume that the net charge on each monomer to be exactly zero (we have noticed up to |0.08|e shifting between monomers), i.e. the parameters of the individual monomer are not transferable, and the parametrisation is best carried out using a larger model. We have considered here a minimal model where the repeat unit is capped with the first and last monomers and alkyl sided chains are replaced by methyl terminations (shown in step 1 of scheme 1). This model was used to compute the force field parameters including atomic point charges and bonded equilibrium parameters through DFT calculations (in this case B3LYP/6-31G*). The model of this size will also alleviate the possible dependency of the intermonomer torsional potential upon the neighbouring monomers or the length of oligomer structure as observed before. We identified the lowest energy conformer for the model oligomer by exhaustive search of all possible cis/trans configuration. Then, a universal DFTbased protocol is used to calculate the intra-and inter-fragment force field parameters (steps 2 and 3 in scheme 1), see SI, sections S1.1 and S1.2 for details. It should be noted that an important feature of this workflow is that each individual intra-fragment bond, angle, and torsion angle equilibrium value is directly taken from the DFT-optimised minimal model, meaning that they are not only determined by the atom types forming the bond/angle/torsion-as is the case in generalised force fields such as OPLS-FF and GAFF , but the entire minimal model structure. This explicit method for bonded parameter calculation maintains the relative atomic positions (within each monomer) close to the real conjugated monomer structure during MD simulations. This feature is essential for the expected accuracy in calculating the electronic structures of SCP models (made by MD) due to the significance of relative atomic positions on the molecular orbital. The choice for DFT functional/basis set (in this version: B3LYP/6-31G*) was made to be consistent with the follow-up QC calculations which will be done directly on the MD snapshots as explained in section 2.3. Also, note that the workflow is designed to be adaptable, should different density functional or parent force field become desirable. The key point is that the protocol and choices are made once to be used consistently for all polymers modelled in one study.