Interfacial ion solvation: Obtaining the thermodynamic limit from molecular simulations

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Molecular Dynamics

Background:

• Macroscopic solution properties are difficult to infer from molecular simulations due to computational limitations.
• Finite size effects, particularly from long-ranged electrostatic interactions, significantly impact simulation accuracy, especially in aqueous solutions.
• Previous work highlighted slow attenuation of these effects with increasing system size.

Purpose of the Study:

• To develop and validate corrections for finite size effects in molecular simulations, focusing on solvation free energies near interfaces.
• To adapt existing methods for bulk solutions to address the unique challenges of interfacial solvation.
• To establish a reliable method for extrapolating simulation results to the thermodynamic limit.

Main Methods:

• Utilized dielectric continuum theory to model long-wavelength solvent response, addressing finite size effects.
• Applied a periodic slab model of liquid coexisting with vapor to calculate solvation free energies for ions.
• Incorporated solvent charge asymmetry corrections for aqueous systems.

Main Results:

• Developed a novel finite size correction for solvation free energies applicable to interfacial systems.
• Demonstrated that the new correction accurately predicts variations in solvation free energy with simulation cell dimensions for a model polar solvent.
• Showed that accounting for solvent charge asymmetry is crucial for accurate corrections in aqueous systems.

Conclusions:

• The proposed finite size corrections accurately account for system size variations in solvation free energies.
• This work provides a straightforward method for extrapolating molecular simulation data to the thermodynamic limit.
• The findings validate the applicability of dielectric continuum theory down to the nanometer scale for describing solvent behavior.