Mean ionic activity coefficients in aqueous NaCl solutions from molecular dynamics simulations

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Materials Science

Background:

• Accurate prediction of electrolyte solution properties is crucial for chemical process design.
• Molecular dynamics simulations offer a powerful tool for investigating thermodynamic properties at the molecular level.

Purpose of the Study:

• To evaluate the accuracy of common non-polarizable water and ion models in predicting mean ionic activity coefficients and solubility of NaCl solutions.
• To assess the thermodynamic consistency of simulation results using the Gibbs-Duhem equation.

Main Methods:

• Molecular dynamics (MD) simulations were performed on aqueous NaCl solutions at 298.15 K and 1 bar.
• Ion pair interactions were gradually introduced to calculate mean ionic activity coefficients.
• Gibbs-Duhem equation was applied to confirm thermodynamic consistency.

Main Results:

• Most model combinations correctly predicted the trends of mean ionic activity coefficients but overestimated values at high salt concentrations.
• All tested models underpredicted NaCl solubility, some significantly.
• Thermodynamic consistency was confirmed for the calculated activity coefficients.

Conclusions:

• Existing non-polarizable water and ion models require improvement for accurate prediction of NaCl solution properties, especially at high concentrations.
• Further development of molecular models is essential for reliable simulation-based predictions in electrolyte systems.
• The study highlights limitations in current models for predicting both activity coefficients and solubility.