Solvation properties of a polarizable water model in a NaCl solution: Monte Carlo isothermal–isobaric ensamble simulations

Abstract

Isothermal–isobaric ensamble Monte Carlo simulations have been carried out for a dilute NaCl aqueous solution at 25 °C and 1 atm, using the transferable intermolecular potential 4-point-fluctuating charge (TIP4P-FQ) water model. The thermodynamic properties such as energy, density and enthalpy of solution were calculated. Structural features of the solvation shells around the Na + and Cl − ions were studied by analyzing the radial distribution functions, the orientational distribution functions, the shell average of the number of water H-bonds and the shell average of the water electric dipole moment. Contributions of the ion, the first shell and bulk water molecules interactions to the total energy were analyzed in terms of the solvation shell structure around the sodium and chlorine ions in solution. The TIP4P-FQ model allows studying water polarization, which cannot be analyzed by means of the rigid models. Evidence of a more ordered structure around the sodium ion than around the chlorine ion is found. Water molecules noticeably increase their dipole moment in the first solvation shell and long-range effects are observed in the bulk water molecules due to the presence of both ions in the solution.