First-principles Determination of Electronic Charge Transport Properties in Polymer Dielectrics Using a Crystalline-based Model System

There are various models for describing the charge transport in polymers but it is unclear how to choose the appropriate one for a given system. In this study, we determine the relevant charge transfer model for several insulating polymers by evaluating the Marcus parameters for electron and hole transfer with the aid of first-principles calculations. As expected, except for electron transfer in polyethylene and isotactic polypropylene, non-adiabatic (polaron) hopping takes place in most polymers, owing to the small inter-chain electronic interactions (10-100 meV) and large polaron formation energy (100-1000 meV). Therefore, the first-principles based parameter-free, multi-scale modeling approach, which we developed for evaluating the hole transfer property in polyethylene, can be used to study the electronic carrier transport properties in wide variety of polymers. The computed Marcus parameters imply that the electron and hole mobilities in syndiotactic polystyrene and polytetrafluoroethylene are larger than the hole mobility in polyethylene and isotactic polypropylene, which agrees with experimental data. The strong chain-length dependence of the computed Marcus parameters indicates that slight change in the polymer structure can result in significant variations in the charge mobility.