  Room-temperature ionic liquids (RTILs) stand out among molecular liquids for
their rich physicochemical characteristics, including structural and dynamic
heterogeneity. The significance of electrostatic interactions in RTILs results
in long characteristic length- and timescales, and has motivated the
development of a number of coarse-grained (CG) simulation models. In this
study, we aim to better understand the connection between certain CG
parametrization strategies and the dynamical properties and transferability of
the resulting models. We systematically compare five CG models: a model largely
parametrized from experimental thermodynamic observables; a refinement of this
model to increase its structural accuracy; and three models that reproduce a
given set of structural distribution functions by construction, with varying
intramolecular parametrizations and reference temperatures. All five CG models
display limited structural transferability over temperature, and also result in
various effective dynamical speedup factors, relative to a reference atomistic
model. On the other hand, the structure-based CG models tend to result in more
consistent cation-anion relative diffusion than the thermodynamic-based models,
for a single thermodynamic state point. By linking short- and long-timescale
dynamical behaviors, we demonstrate that the varying dynamical properties of
the different coarse-grained models can be largely collapsed onto a single
curve, which provides evidence for a route to constructing
dynamically-consistent CG models of RTILs.
