A simple, parameter-free method for computing solvation free energies of ions

Area of Science:

• Computational Chemistry
• Molecular Dynamics Simulations
• Physical Chemistry

Background:

• Calculating solvation free energies for ions is complex due to long-range Coulomb interactions in molecular dynamics (MD) simulations.
• Existing approximations for small systems lack robustness, hindering accurate free energy determination.

Purpose of the Study:

• To develop a robust and reliable method for calculating ion solvation free energies using MD simulations.
• To address the limitations of current approximations and corrections in solvation free energy calculations.

Main Methods:

• Employing spherical boundary conditions with a buffer zone to circumvent the need for boundary corrections.
• Simulating ion solvation in water droplets of approximately 21 Å.
• Testing convergence and independence from water confinement or ion restraint parameters.

Main Results:

• The proposed method accurately calculates solvation free energies without requiring boundary corrections.
• Results demonstrate convergence at a droplet size of 21 Å and independence from simulation parameters.
• The method was successfully applied to calculate solvation free energies of charged amino acid side chain analogs.

Conclusions:

• The novel approach using spherical boundary conditions and a buffer zone provides a robust solution for ion solvation free energy calculations.
• This method enhances confidence in determining force field parameters from simulations.
• Similar accurate results were obtained when tested with periodic boundary conditions.