(709c) A Combined Classical MD and DFT Approach for Modeling Ionic Adsorption on Metal Electrodes with Explicit Description of the Electrical Double Layer.

Electrocatalytic charge transfer reactions are fundamentally affected by interfacial phenomena such as solvation and electrification. Modeling these interfacial effects requires extensive sampling of the phase space of the electrolyte (e.g. water and ions) within the compact electrical double layer (EDL). Ab initio molecular dynamics (AIMD) can explicitly simulate the double layer yet fails to capture its associated slow dynamics due to its high computational cost. Implicit solvation models offer a continuum description of the electrolyte that incur much less computational cost but omit important explicit electrolyte structuring. Classical MD has better spatial and temporal sampling of the atomistic electrolyte yet lacking description of chemical bonds forming/breaking. In this presentation, we present our MD approach for modeling an explicitly atomistic double layer, then subsequently combining it with DFT calculations to gain insights into the effect of the EDL on the ionic adsorption process. We first outline the dynamics and polarizability of solvent water from classical MD simulations. The dynamics of the first water adlayer are highly restricted, having prolonged translational and rotational characteristic timescale up to a factor of 4 and 20, respectively, compared to bulk water. The dielectric response of water in the double layer is markedly anisotropic, enhanced in the in-plane direction (ε≈110) and suppressed in the out-of-plane direction (ε≈3). Next, we use DFT to model the adsorption of Na⁺ and Cl^- on Ag(111) surface with minimal description of the EDL (solvated with a few explicit water or with a continuum model). Subsequently, the DFT-treated adsorbed ions are embedded into the classical MD simulation of the EDL to elucidate the hydration properties of the ions at different applied potentials. This multi-scale study both enables better atomistic understanding of the EDL and its effect on ionic adsorption, and potentially allows for investigating other electrocatalytic charge transfer reactions.