We begin the model reduction of semiconducting polymers by observing that conjugated polymers are made of relatively rigid monomers which retain their local structures regardless of the overall chain conformation. A recent exploration of the electronic structures of 36 donor-acceptor copolymers has confirmed that the valence band orbital of semiconducting polymer can be described, with very few exceptions, as a linear combination of the highest occupied molecular orbitals (HOMOs) localized on individual monomer. Consequently the first step of our model reduction scheme is the construction of an electronic structure model of the polymer chain considering only one orbital per monomer, the HOMO of each monomer as we are focusing exclusively on hole transport (see bottom panel of Fig. ).