First-Principles, Physically Motivated Force Field for the Ionic Liquid [BMIM][BF4].

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Materials Science

Background:

• Molecular simulations are crucial for understanding structure-property relationships in complex fluids.
• Accurate and transferable classical force fields are essential for simulating large systems and long timescales.
• Room-temperature ionic liquids (RTILs) present unique challenges due to their complex interactions.

Purpose of the Study:

• To develop a physically motivated and transferable classical force field for 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]).
• To validate the force field's accuracy by comparing simulation predictions with experimental data for key physical properties.
• To analyze the underlying intermolecular interactions, particularly polarization and charge transfer, in [BMIM][BF4].

Main Methods:

• Development of a force field based on symmetry-adapted perturbation theory (SAPT).
• Utilizing molecular dynamics (MD) simulations to predict thermophysical properties.
• Performing explicit energy decomposition to quantify intermolecular interactions.

Main Results:

• MD simulations using the new force field accurately predicted liquid density, enthalpy of vaporization, diffusion coefficients, viscosity, and conductivity of [BMIM][BF4].
• The force field achieved excellent agreement with experimental data without employing adjustable parameters.
• Analysis revealed the critical role of polarization and minimal charge transfer in the interactions within [BMIM][BF4].

Conclusions:

• The developed force field provides a highly accurate and physically grounded representation of [BMIM][BF4].
• The findings challenge the common practice of scaling down charges in ionic liquid simulations.
• The first-principles parametrization suggests excellent transferability to other ionic liquids and conditions, advancing molecular simulation capabilities.