Is Charge Scaling Really Mandatory when Developing Fixed-Charge Atomistic Force Fields for Deep Eutectic Solvents?

In recent years, molecular dynamic simulations on choline chloride based deep eutectic solvents (DES) have flourished. Most of these studies point to the fact that in order to accurately reproduce dynamical properties of the latter using a fixed-charge atomistic force field (FF) one has to resort to charge scaling. In this work, we propose an alternative to charge scaling and show that the sole refinement of the Lennard-Jones parameters of the oxygen and hydrogen of the hydroxyl function in the GAFF v2.11 FF enables an accurate description of static, dynamical, and structural properties of two commonly used DES, namely, ethaline (1:2 mixture of choline chloride and ethylene glycol) and glyceline (1:2 mixture of choline chloride and glycerol). Various computed physicochemical properties for both mixtures with our modified version of the GAFF v2.11 FF are found in good agreement with experimental data. Most importantly, however, is the fact that self-diffusion coefficients for the various components of both ethaline and glyceline are found within a maximum deviation of 33% from experimental values, which is at least as good if not better than current scaled-charge FF. Finally, computed radial distribution functions match with those reported in the literature.