Simulation of polymeric mixed ionic and electronic conductors with a combined classical and quantum mechanical model

In organic polymeric materials with mixed ionic and electronic conduction (OMIEC), the excess charge in doped polymers 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 encountered in this type of materials, 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, but additional features should be added to the model to enable the study of processes such as electrochemical doping.

Automated summary

In organic polymeric materials with mixed ionic and electronic conduction, the dynamics of the polymer chain cannot be accurately described with a model including only fixed point charges. A scheme based on the combination of MD and QM/MM was constructed 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. The results indicate the importance of capturing the correlated motions of excess charge and ions in order to understand the phenomenology of these materials.