Molecular dynamics simulation of solvent reorganization in ion transfer reactions near a smooth and corrugated surface

We study the influence of different metal-water potentials on the energetics of ion transfer reactions at metal electrodes by extensive molecular dynamics simulations. The (slope of the) barrier for both ion and atom adsorption is found to be higher for a corrugated metal-water potential compared to a smooth metal-water potential, due to the more rigid water structure caused by the former potential. Interestingly, between 4 and 6 A from the surface, the free energy profiles are the same for both ion and atom, suggesting that the displacement of the water from the surface makes the largest contribution to the free energy of adsorption. Although the parameters for solvent reorganization related to the ion/atom transfer depend critically on the details of the metal-water potential, this is much less so for the solvent reorganization due to electron transfer. The small differences observed in solvent reorganization energy and charge transfer are due to the different simulation boxes used for the two different potentials, rather than to intrinsically different energetics. Therefore, solvent reorganization related to electron transfer is primarily governed by long-range electrostatic effects, whereas solvent reorganization related to ion transfer is primarily governed by much shorter-range solvent structural effects existing at the electrode -electrolyte interface.