Reactive Bottom-up Coarse-Grained Model for Hydrated Protons

Proton transport plays a critical role in many areas of chemistry, physics, biology, and materials science. Since proton transport occurs at a wide range of spatiotemporal scales, from the quantum to the mesoscopic levels, it is an intrinsically multiscale phenomenon. Yet, developing a high-fidelity multiscale model for hydrated protons is a challenge and currently limited to the atomistic level due to reactive bonding from explicit proton shuttling. This work aims to greatly extend the investigation of hydrated protons across much larger and longer scales by developing a rigorous bottom-up coarse-grained model to recapitulate structure and dynamics at a reduced level. The unique structural correlations arising from the hydronium cation can be captured by introducing internal states to the coarse-grained sites derived from quantum mechanics. A systematic design principle will be presented for determining internal states. To correctly capture the dynamics of hydrated protons, the average medium friction coefficient was predicted under Markovian limits. Our new Hydronium Ultra-coarse-grained Model with Improved Dynamics (HUMID) can faithfully capture structural and dynamical properties, including diffusion and hydronium time correlation functions with a speed-up factor of 500. As the first of its kind, this model can serve as an exciting foundation for studying mesoscale phenomena governed by proton transport and provide design principles for general reactive CG models with complex dynamics.