Pairwise-additive force fields for selected aqueous monovalent ions from adaptive force matching.

Area of Science:

• Computational chemistry
• Physical chemistry
• Materials science

Background:

• Accurate molecular simulations require reliable force fields.
• Developing accurate potentials for simple ions is crucial for understanding electrolyte solutions.
• Existing potentials may not capture the nuances of ion-solvation interactions.

Purpose of the Study:

• To develop simple, non-polarizable potentials for Na(+), K(+), Cl(-), and Br(-) ions.
• To validate the developed potentials by comparing simulated properties with experimental data.
• To investigate ion behavior at interfaces in electrolyte solutions.

Main Methods:

• Adaptive Force Matching (AFM) method was employed.
• Ab initio MP2 (Møller–Plesset perturbation theory) calculations served as the reference.
• Molecular dynamics simulations were performed using the developed potentials.

Main Results:

• The MP2-AFM force field achieved <5% error in predicting solvation free energies for four salts.
• Calculated ion-water radial distribution functions and water tilt angles showed good agreement.
• Ion diffusion constants were within 6% of experimental values.
• Concentration-dependent water diffusion and surface tension were accurately reproduced.
• Bromide ion interface behavior varied with concentration (enrichment at 1.6M KBr, repulsion at lower concentrations).

Conclusions:

• The developed non-polarizable force field offers a computationally efficient and accurate representation of Na(+), K(+), Cl(-), and Br(-) in aqueous solutions.
• The potential accurately captures key thermodynamic and dynamic properties of these electrolytes.
• The model provides insights into ion-surface interactions, highlighting concentration-dependent effects.