Incorporating excluded solvent volume and physical dipoles for computing solvation free energy

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Molecular Dynamics

Background:

• The Born equation approximates solvation free energy using solute properties and solvent dielectric constant.
• Discrepancies exist between Born equation predictions and molecular dynamics (MD) simulations regarding dielectric polarization.
• Adjusting Born radii alone is insufficient for accurate solvation free energy across solute conformations.

Purpose of the Study:

• To develop a more accurate model for dielectric polarization around solutes in MD simulations.
• To derive a new equation for solvation free energy that incorporates a refined solvent model.
• To validate the derived equation against experimental data for ionic solvation.

Main Methods:

• Modeled first-shell water molecules as physical dipoles within a van der Waals sphere.
• Treated intermediate water molecules as bulk solvent.
• Represented first-shell water dipoles using surface charge layers with variable separation distances based on orientational distribution functions.
• Derived a new equation for solvation free energy using the TIP3P water model.

Main Results:

• The derived equation accurately describes the solvation free energy of ions.
• Calculated solvation free energies show good agreement with experimental values.
• The refined solvent model effectively mimics dielectric polarization in MD simulations.

Conclusions:

• The proposed solvent model and derived equation offer improved accuracy for solvation free energy calculations.
• This method provides a better representation of the solute-environment electrostatic interactions.
• The findings have implications for accurate molecular simulations in chemistry and related fields.