Effects of Ion-Water Potentials in Molecular Dynamics Simulation of Ion Distribution in Nanochannels

Abstract

Understanding ion and fluid transport through highly confined nanochannels is important for the study of many interesting phenomena in nature and for the design of novel nanofluidic devices. Molecular dynamics has been proved to be a powerful tool to investigate the transport of ion and fluid in nanochannels, however, the results of molecular dynamics simulation depend on the selection of intermolecular potentials in the simulation. In this work, we applied two different ionwater interaction potentials to study their effects in the molecular dynamics simulation of ion distribution in the nanochannels between two parallel charged surfaces. Water was simulated with the TIP4P and SPC/E models and the electrostatic interaction between ions, water molecules, and surface charges was modeled by using Ewald summation algorithm with the slab correction. Two different interaction potentials between the ion and water molecules, one based on simple Lennard-Jones potential and the other based on the Bounds' ion-water potential, were adopted to explore the effects of ion-water interactions on the ion distribution in nanochannels. The Bounds' model takes into account the interactions between ions and both oxygen and hydrogen atoms in the water molecules. Ion concentration profiles in nanochannels with these two different potentials were calculated and results showed that the ion-water interaction potential could significantly affect the ion distribution in nanochannels. We expect that the ion-water potential could also have important effect on modeling of electroosmotic flow through nanochannels.