Comparison between Ab Initio Molecular Dynamics and OPLS-Based Force Fields for Ionic Liquid Solvent Organization

Abstract

OPLS-based force fields (FFs) have been shown to provide accurate bulk-phase properties for a wide variety of imidazolium-based ionic liquids (ILs). However, the ability of OPLS to reproduce an IL solvent structure is not as well-validated given the relative lack of high-level theoretical or experimental data available for comparison. In this study, ab initio molecular dynamics (AIMD) simulations were performed for three widely used ILs: the 1-butyl-3-methylimidazolium cation with chloride, tetrafluoroborate, or hexafluorophosphate anions, that is, [BMIM]­[Cl], [BMIM]­[BF4], and [BMIM]­[PF6], respectively, as a basis for further assessment of two unique IL FFs: the ±0.8 charge-scaled OPLS-2009IL FF and the OPLS-VSIL FF. The OPLS-2009IL FF employs a traditional all-atom functional form, whereas the OPLS-VSIL FF was developed using a virtual site that offloads negative charge to inside the plane of the ring with careful attention given to reproducing hydrogen bonding. Detailed comparisons between AIMD and the OPLS FFs were made based on radial distribution functions (RDFs), combined distribution functions (CDFs), and spatial distribution functions (SDFs) to examine cation–anion interactions and π+–π+ stacking between the imidazolium rings. While both FFs were able to correctly capture the general solvent structure of these popular ILs, the OPLS-VSIL FF quantitatively reproduced interaction distances more accurately. In addition, this work provides further insights into the different short- and long-range structure patterns of these popular ILs.

Uncovering the Critical Factors that Enable Extractive Desulfurization of Fuels in Ionic Liquids and Deep Eutectic Solvents from Simulations

“…The adjustable parameters are the force constants k , the r o and θ o equilibrium bond and angle values, Fourier coefficients V , partial atomic charges, q , and Lennard-Jones radii and well-depths, σ and ε. In this work, IL FF parameters were taken from ±0.8 charge-scaled OPLS-2009IL , and the virtual site OPLS–VSIL − (Tables S1–S4) and the DES FF parameters came from OPLS–DES. , All FF parameters are available to download at and as preformatted GROMACS files. The cyclic sulfur compounds OPLS-AA parameters were generated using the 1.14*CM1A-LBCC charge model through the LigParGen web server …”

A Systematic Study on the Role of Hydrogen Bond Donors in Dictating the Dynamics of Choline-Based Deep Eutectic Solvents

“…This is a brief description of the methodology used to simulate three different compositions of deep eutectic solvents (DESs) containing ammonium thiocyanate using the GROMACS 2021 package . The force fields for the DES components, choline chloride and ethylene glycol, and the acids are taken from the work of Doherty et al In that work, the force fields were modified to include a charge scaling to account for polarization effects. , The force field parameters for ammonium thiocyanate are taken from Zheng et al…”

“…28 The force fields for the DES components, choline chloride and ethylene glycol, and the acids are taken from the work of Doherty et al 29 In that work, the force fields were modified to include a charge scaling to account for polarization effects. 30,31 The force field parameters for ammonium thiocyanate are taken from Zheng et al 32 The simulation box is created using a 50 × 50 × 50 Å 3 box, 33 and the DES components and ammonium thiocyanate are randomly placed using the Packmol package maintaining the experimental composition. In the case of DES1, 400 molecules of ChCl and 800 molecules of EG are packed in the box, while for DES2 and DES3, 400 molecules of ChCl and 400 molecules of carboxylic acid are packed in the box to maintain the DES composition.…”

Atomistic molecular dynamics simulation and COSMO-SAC approach for enhanced 1,3-propanediol extraction with imidazolium-based ionic liquids

“…The equations of motion were integrated numerically using the velocity-Verlet algorithm with a time step of 1.0 fs. The LINCS algorithm was used to constrain covalent bonds to hydrogen atoms, maintaining their stability throughout the simulation (65). For long-range electrostatic interactions, the PPPM (Particle-Particle Particle-Mesh) method was employed (66).…”