Revisiting OPLS Force Field Parameters for Ionic Liquid Simulations

Abstract

Our OPLS-2009IL force field parameters (J. Chem. Theory Comput. 2009, 5, 1038-1050) were originally developed and tested on 68 unique ionic liquids featuring the 1-alkyl-3-methylimidazolium [RMIM], N-alkylpyridinium [RPyr], and choline cations. Experimental validation was limited to densities and a few, largely conflicting, heat of vaporization (ΔH) values reported in the literature at the time. Owing to the use of Monte Carlo as our sampling technique, it was also not possible to investigate the reproduction of dynamics. The [RMIM] OPLS-2009IL parameters have been revisited in this work and adapted for use in molecular dynamics (MD) simulations. In addition, new OPLS-AA parameters have been developed for multiple anions, i.e., AlCl, BF, Br, Cl, NO, PF, acetate, benzoate bis(pentafluoroethylsulfonyl)amide, bis(trifluoroethylsulfonyl)amide, dicyanamide, formate, methylsulfate, perchlorate, propanoate, thiocyanate, tricyanomethanide, and trifluoromethanesulfonate. The computed solvent densities, heats of vaporization, viscosities, diffusion coefficients, heat capacities, surface tensions, and other relevant solvent data compared favorably with experiment. A charge scaling of ±0.8 e was also investigated as a means to mimic polarization and charge transfer effects. The 0.8-scaling led to significant improvements for ΔH, surface tension, and self-diffusivity; however, a concern when scaling charges is the potential degradation of local intermolecular interactions at short ranges. Radial distribution functions (RDFs) were used to examine cation-anion interactions when employing 0.8*OPLS-2009IL and the scaled force field accurately reproduced RDFs from ab initio MD simulations.

How imidazolium‐based ionic liquids solubilize the poorly soluble ibuprofen? A theoretical study

“…Nevertheless, Coutinho et al pointed out that π–π stacking between the imidazolium cation and ibuprofen did not exist. To further prove the π–π stacking, the CDFs between imidazolium cations and ibuprofen are calculated, which can provide more information on the π–π stacking by monitoring both the distance, R , and the angle, α , as shown in Figure . The CDF was computed in the following way: the RDF were expanded in a second dimension that corresponds to the tilt angle α , that is, .…”

Thermodynamic, structural and dynamic properties of ionic liquids [C4mim][CF3COO], [C4mim][Br] in the condensed phase, using molecular simulations

“…10,11 Recent publications have stressed the existence of multiple shortcomings in some of the available classical FF, including inadequate solvent dynamics, errors in the prediction of hydrogen-bonding strength, inadequate mixture phase behavior, and errors in solvent structure and interactions. [12][13][14][15] Recent contributions have modied the atomic partial charges and Lennard-Jones parameters, in computer simulations by considering the dielectric constant as a target property in order to mimic the miscibility observed experimentally between two different liquids. 16,17 In the literature, there is a constant need for reliable and accurate IL FF 14,18,19 able to capture, among others, the local electrostatic properties, 20 microscopic dynamics, 21 and vibrational spectra; 22 as indicated by Maginn, 18 many FFs already published have not been validated yet against reliable and sensitive properties such as enthalpy of vaporization, and dynamic properties.…”

“…The lack of an accurate classical FF for predicting thermodynamic, structural, and transport properties for specic substances hinders the design of new ILs solvents for condensed applications. Different research groups 13,[23][24][25][26][27][28][29][30][31] have developed classical FFs for different ILs and evaluated their capabilities to predict different properties such as: density, enthalpy of vaporization, surface tension, heat capacity at constant pressure, cohesive energy, structural properties, and in a reduced extent, properties such as: VLE curves, self-diffusion coefficients, dielectric constants, thermal conductivities, viscosities, etc. A comprehensive review regarding the prediction of thermodynamic, structural, and dynamic properties of ILs, using Molecular Dynamics simulations can be found in Batista et al 6 and references therein.…”

Computational Spectroscopy of Ionic Liquids for Bulk Structure Elucidation

“…Depending on the atomic resolution, it is possible to have fully atomistic (FA) or coarse‐grained (CG) versions. A popular FF of the first type for ILs has been developed by Canongia‐Lopes and Padua; nonetheless, there is still an active research in this area that cannot be thoroughly covered here. Coarse‐graining reduces the number of explicit sites, thus reducing the computer power needed, so it is an interesting option for ILs where strong electrostatic interactions require long simulation times (because of the slow dynamics) and large simulations boxes (because of the large spatial correlations related to microphase separation).…”