Coarse-Grained Molecular Dynamics of Polymer Electrolytes Using Drude Oscillators

Ion-polymer interactions in polymer electrolytes must be strong enough to solvate ions and allow for separate cation and anion motion, however, very strong local interactions slow ion dynamics and reduce conductivity. We use generic models and molecular dynamic simulations to understand these effects and suggest strategies to design improved materials. In prior work, we have used an isotropic ion-polymer potential form to reproduce features of ion solvation. However, this does not include polarizability or effects of locally varying dielectric strength due to different polymer and ion densities. In atomistic simulations, polarizability can be included using Drude oscillators, in which an atom is represented by a core bonded to a Drude particle of opposite charge via a strong harmonic spring. We embed Drude oscillators into each polymer bead of our coarse-grained model and study ion-containing polymers with a range of polarizabilities. The calculated dielectric constant from simulations shows a good match with the Clausius–Mossotti equation at low enough polarizability, and the calculated solvation energy agrees with the Born relation. The potential for simulating copolymer systems in this manner will also be discussed.