Due to the negative environmental impact of damaging organic solvents, there is an increasing interest in a set of environmentally-friendly solvents known as ionic liquids (ILs) and deep eutectic solvents (DES). These solvents, primarily composed of ions, provide numerous advantages from both chemical and environmental perspectives. Despite the excitement, a fundamental understanding of how they operate is still lacking, but can be studied with the aid of molecular dynamics simulations. To properly simulate each system, sets of nonpolarizable parameters have been developed (OPLS-2009IL, OPLS-VSIL, and OPLS-DES). Emphasis was put on predicting experimental data while maintaining the complex hydrogen bond network, specifically with imidazolium and choline chloride containing systems. Enhancement came from the optimization of nonbonded parameters, including scaling of charges to mimic polarization, scaling of Lennard-Jones terms to control interaction strength between ions, and inclusion of a virtual site in the imidazolium cation to better represent a proper resonance structure. Molecular dynamics simulations with each force field accurately reproduced experimental bulk-solvent properties. Solvent-solvent interactions were monitored using radial, spatial, and combined distribution functions that matched <i>ab initio</i> molecular dynamics (AIMD) and experimental liquid-phase neutron diffraction data. Local interactions, including cation-anion hydrogen bonding and π−π  stacking between the imidazolium rings, were also accurately reproduced.

Development of OPLS-AA force field parameters for ionic liquid and deep eutectic solvent simulations

2019 Spring National Meeting

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