Self-Consistent Scheme Combining MD and Order-N DFT Methods: An Improved Set of Nonpolarizable Force Fields for Ionic...

Area of Science:

• Computational Chemistry
• Materials Science
• Physical Chemistry

Background:

• Nonpolarizable force fields are crucial for simulating ionic liquids.
• Accurate atomic charges are essential for reliable force field performance.
• Existing methods may not fully capture many-body charge transfer effects.

Purpose of the Study:

• To develop and validate a self-consistent scheme combining molecular dynamics (MD) and density functional theory (DFT) for tuning nonpolarizable force fields.
• To investigate the impact of DFT-derived atomic charges on energetic and transport properties of ionic liquids.
• To assess the performance of the refined force fields for imidazolium-, pyrrolidinium-, and ammonium-based ionic liquids.

Main Methods:

• A self-consistent scheme integrating MD simulations with order-N DFT calculations.
• Determination of atomic charges using the entire MD cell for DFT, accounting for many-body effects.
• Application to various ionic liquid compositions (imidazolium, pyrrolidinium, ammonium).

Main Results:

• DFT-derived charges show greater variation with ionic liquid composition than thermodynamic conditions.
• The refined force fields significantly improve predictions of transport properties (self-diffusion, conductivity, viscosity).
• Weakened inter-ionic interactions due to effective charges enhance fluidity and correct overly slow dynamics.

Conclusions:

• The MD-DFT self-consistent scheme provides an effective alternative to explicitly many-body models for ionic liquids.
• This approach enhances the accuracy of nonpolarizable force fields, particularly for transport properties.
• The method offers a robust way to describe the condensed-phase behavior of ionic liquids.