Influence of Polarizability on the Structure, Dynamic Characteristics, and Ion-Transport Mechanisms in Polymeric Ionic Liquids

We used atomistic simulations and compared the prediction of three different implementations of force fields, namely, the original full partial charge system, the scaled partial charge system, and the Drude oscillator polarizable force field and its effect on the structural and dynamic properties of a polymeric ionic liquid, poly(1-butyl-3-methyl-imidazolium hexafluorophosphate). We found that both the scaled and the polarizable force field models yield comparable predictions of structural and dynamic properties, although the scaled charge model artificially lowers the first-neighbor peak of the radial distribution function and therefore leads to a slight reduction in density. The full charge model was not accurate in its prediction of the dynamic properties but could reproduce the structural properties. With a refined analysis method for the ion-hopping mechanisms, we found that all three methods produce very similar conclusions, namely, that the mobile anion is associated with three cations from two distinct polymer chains and that the fractions of inter- and intramolecular hopping events are comparable. Our results demonstrate that the scaled charge force fields provide a computationally efficient means to capture polarizability effects on both the structural and dynamic properties of polymeric ionic liquid systems.