Molecular Dynamics Simulation of Aqueous Sodium Chloride Solution at the NaCl(001) Interface with a Polarizable Water Model

The sodium chloride solution−NaCl crystal interface serves as an example of aqueous electrolytes at uncharged ionic surfaces and plays an important role in technologically relevant processes and atmospheric chemistry. This interface is investigated by classical molecular dynamics simulations at ambient pressure and generally at 298 K. A fluctuating charges version of the extended simple point charge (SPC/E) water model, the SPC/E-P model, is used to calculate structural and dynamical properties of the ions at the interface and in the bulk solution: density profiles and potentials of mean force including concentration and temperature dependencies, hydration numbers, lateral structures, and mobilities of ions parallel and perpendicular to the interface. We find that sodium ions are adsorbed selectively at the metastable NaCl(001) interface, and their mobility is strongly reduced due to adsorption. Analogous calculations using the nonpolarizable SPC/E model do not exhibit such an intense exothermic sodium ion adsorption; i.e., solvent polarization can significantly affect ionic distributions close to polar but uncharged interfaces. In the case of SPC/E-P water, dipole moment profiles are calculated also.