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

Song Hi Lee,Bryan M Wong

doi:10.1155/2020/6661196

Abstract

We present the result of molecular dynamics (MD) simulations to calculate the molar conductivity Λ m = λ N a + + λ C l − 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 i i (r) with κ = 0.10 Å−1 show a dramatic change with a very deep minimum of g NaCl (r) and, as a result, sharp maxima of g NaNa (r) and g 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.

Highlights

Where the limiting molar conductivities of Na+ and Cl− at 25oC are measured as 5.01 and 7.63 mS m2 mol−1 experimentally [1]
DNa+ and DCl− at 25°C in SPC/E water were obtained from mean square displacements (MSDs), equation (9), of Na+ and Cl− from our molecular dynamics (MD) simulations using Ewald sum with κ 0.05–0.25 A −1 employing a velocity Verlet algorithm
We have carried out molecular dynamics (MD) simulations of NaCl in SPC/E water at 25°C to calculate the molar conductivity Λm of NaCl as a function of NaCl concentration (c) using Ewald sums employing a velocity Verlet algorithm

Summary

Molecular Models and Molecular Dynamics Simulation Details

For c 1 mol/L of NNaCl 36 with V 36000 cm3/NA, ρt 18.0152Nw + 36 × 58.443􏼁/36000􏼐g/cm3􏼑. (5). For c 1 mol/L of NNaCl 36 with V 36000 cm3/NA, ρt 18.0152Nw + 36 × 58.443􏼁/36000􏼐g/cm3􏼑. %WNaCl (36 × 58.443)/ 18.0152Nw +(36 × 58.443)􏼁 × 100. Substituting equations (5) and (6) into equation (4), we obtain Nw 1956. E SPC/E model [10] was adopted for water-water and ion-water. E pair potential between water and ion has the TIPS form [11]: viw. Where σio and εio are Lennard–Jones (LJ) parameters between oxygen on a water molecule and an ion i, qj is the charge at site j in water, and qi is the charge on ion i

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Results and Discussion

Conclusions