Molecular force fields for aqueous electrolytes: SPC/E-compatible charged LJ sphere models and their limitations

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Materials Science

Background:

• Accurate molecular models are crucial for simulating aqueous electrolyte solutions.
• Sodium chloride (NaCl) solutions are fundamental in various chemical and biological systems.
• Existing force fields often struggle to reproduce experimental properties of NaCl solutions at different concentrations.

Purpose of the Study:

• To assess the predictive accuracy of thirteen common force fields for aqueous NaCl solutions.
• To evaluate the performance of these force fields in predicting solution density, chemical potential, and salt solubility.
• To identify limitations of current force fields for high-concentration and solubility predictions.

Main Methods:

• Utilized the Osmotic Ensemble Monte Carlo method for efficient calculation of solution chemical potential.
• Simulated aqueous NaCl solutions using SPC/E water model and thirteen NaCl force fields.
• Calculated concentration dependence of chemical potential, solution density, and salt solubility at ambient conditions.

Main Results:

• Significant scattering in results across the thirteen force fields was observed.
• None of the force fields accurately predicted properties over the entire concentration range; only two were deemed acceptable.
• Several force fields predicted precipitation below experimental solubility limits, restricting their applicability.

Conclusions:

• Current NaCl force fields show limitations in accurately representing high-concentration solution properties and solubility.
• Improved parameter fitting strategies or the development of more sophisticated force field models are necessary.
• Inaccurate force fields can impact the reliability of biomolecular simulations involving electrolytes.