Organic materials that efficiently couple electronic and ionic charge transport (OMIEC) have been recognized as essential in a wide range of technologies , from energy storage and generation  to nanomedicine and healthcare , thanks to their ease of processing, flexibility, low cost, and because they can be finely tuned, e.g. to ensure perfect integration with cellular tissues for nanomedicine or a light weight for energy storage. Theoretical predictions could represent a great help in developing new materials, tailored for any given application. However, they face the fundamental obstacle that, in these systems, the excess charge is very mobile, and the dynamics of the polymer chain cannot be accurately described with a model including only fixed point charges. Ions and polymer are comparatively slower and a methodology to capture the correlated motions of excess charge and ions is currently unavailable. Considering a prototypical interface for an archetypal OMIEC (poly-thiophene with glycol side chains), we constructed a scheme based on the combination of MD and QM/MM to evaluate the classical dynamics of polymer, water and ions, while allowing the excess charge of the polymer chains to rearrange following the external electrostatic potential . We find that the location of the excess charge varies substantially between chains. The excess charge changes across multiple timescales, as a result of fast structural fluctuations and slow rearrangement of the polymeric chains. Our results indicate that such effects are likely important to describe the phenomenology of OMIEC, and we are working on the introduction of additional features in the model to enable the study of processes such as electrochemical doping.
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