Abstract
Here, we develop and verify the performance of a hybrid molecular modeling approach that combines coarse-grained apolar solvent and atomistic solute or polar solvent description, for example, for description of reverse micellar systems. The coarse-grained solvent model is directly applicable to organic solvents encompassing alkane, alkene, and fatty acid ester functional groups and connects directly to both standard united-atom GROMOS 53A6 and all-atom CHARMM27 force fields, as well as the atomistic detail water models compatible with these force fields. The different levels of description are coupled via explicit, unscaled electrostatics, and scaled mixing rules for dispersive interactions. The hybrid model is in near-quantitative agreement with fully atomistic simulations when combined with the CHARMM27 model but underestimates modestly surfactant aggregation when using GROMOS 53A6 united-atom description. The use of truncated electrostatics affords up to a 9-fold increase in computational speed without significant loss of accuracy. However, long-range electrostatic calculations and load imbalance at high core counts can significantly degrade the performance. We demonstrate the usability of the hybrid model by assessing the reverse micelle formation of a homologous series of nonionic glycerolipids via large-scale self-assembly simulations. The presented model is demonstrated here for accurate description of surfactant systems in apolar solvents, with and without also polar solvent (water) in the system. The formulation can be expected to describe well also other solute species or interfaces with an apolar solvent in an apolar environment.
Highlights
Surfactants in apolar solvents form reverse micellar and emulsion systems that are both technologically and fundamentally significant
The modeling of apolar surfactant systems using current atomistic molecular models is limited in the attainable size and timescales by the computationally taxing nature of atomistic force fields, as well as by the special characteristics of apolar systems, for example, long relaxation times resulting from high solvent viscosity
We coupled the models with two atomistic force fields, namely, GROMOS 53A6 and CHARMM27, and verified the performance
Summary
Surfactants in apolar solvents form reverse micellar and emulsion systems that are both technologically and fundamentally significant. Coarse-grained approaches have enabled, for example, large-scale simulations of lipid membranes,[8,9] protein systems,[10] and predicting structures of polymer systems.[11,12] localized specific interactions, charge correlations, and sensitivity to, for example, hydrogen bonding, which are all often observed in apolar surfactant systems, are challenging for coarse-grained interaction models to capture. This results from the concept relying on employing effective, delocalized interactions to capture molecular system performance
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