Dynamic and Static Properties of Aqueous NaCl Solutions at 25°C as a Function of NaCl Concentration: A Molecular Dynamics Simulation Study

Abstract

We present the result of molecular dynamics (MD) simulations to calculate the molar conductivity ${\mathrm{\Lambda }}_m\left(={\lambda }_{N{a}^{+}}+{\lambda }_{C{l}^{-}}\right)$ of NaCl in SPC/E water at 25°C as a function of NaCl concentration (c) using Ewald sums employing a velocity Verlet algorithm. It is found that the MD result for Λm with Ewald sum parameter κ = 0.10 Å−1 gives the closest one to the experimental data and that the obtained radial distribution functions $g_{ii}$ (r) with κ = 0.10 Å−1 show a dramatic change with a very deep minimum of $g_{\text{NaCl}}$ (r) and, as a result, sharp maxima of $g_{\text{NaNa}}$ (r) and $g_{\text{ClCl}}$ (r) at the distance 9.95 Å, which indicates a characteristic of ionic atmosphere, the basis of the Debye–Hückel theory of ionic solutions. The static and dynamic properties of NaCl (aq) solutions are analyzed in terms of radial distribution functions, hydration numbers, coordination numbers around Na+ and Cl−, residence times of water around Na+ and Cl−, water diffusion, and ion-ion electrostatic energies to explain the behavior of the molar conductivity Λm of NaCl obtained from our MD simulations.