  Even though atomistic and coarse-grained (CG) models have been used to
simulate liquid nanodroplets in vapor, very few rigorous studies of the
liquid-liquid interface structure are available, and most of them are limited
to planar interfaces. In this work, we evaluate several existing force fields
(FF)s, including two atomistic and three CG FFs, with respect to modeling the
interface structure and thermodynamic properties of the water-hexane interface.
Both atomistic FFs are able to quantitatively reproduce the interfacial tension
and the coexisting densities of the experimentally-observed planar interface.
We use the atomistic FFs to model water droplets in hexane and use these
simulations to test the CG FFs. We find that the tested CG FFs cannot reproduce
the interfacial tensions of planar and/or curved interfaces. Finally, we
propose a new approach for learning CG potentials within the CG SDK
(Shinoda-DeVane-Klein) FF framework from atomistic simulation data. We
demonstrate that the new potential significantly improves the prediction of
both the interfacial tension and structure of water-hexane planar and curved
interfaces.
