Deep Eutectic Solvents: Molecular Simulations with a First-Principles Polarizable Force Field

The
unique properties of deep eutectic solvents make them useful
in a variety of applications. In this work we develop a first-principles
force field for reline, which is composed of choline chloride and
urea in the molar ratio 1:2. We start with the symmetry adapted perturbation
theory (SAPT) protocol and then make adjustments to better reproduce
the structure and dynamics of the liquid when compared to first-principles
molecular dynamics (FPMD) simulations. The resulting force field is
in good agreement with experiments in addition to being consistent
with the FPMD simulations. The simulations show that primitive molecular
clusters are preferentially formed with choline–chloride ionic
pairs bound with a hydrogen bond in the hydroxyl group and that urea
molecules coordinate the chloride mainly via the trans-H chelating
hydrogen bonds. Incorporating polarizability qualitatively influences
the radial distributions and lifetimes of hydrogen bonds and affects
long-range structural order and dynamics. The polarizable force field
predicts a diffusion constant about an order of magnitude larger than
the nonpolarizable force field and is therefore less computationally intensive. We hope this study paves the way for
studying complex hydrogen-bonding liquids from a first-principles
approach.