  Recently, we introduced a new force field (FF) to simulate transport
properties of imidazolium-based room-temperature ionic liquids (RTILs) using a
solid physical background. In the present work, we apply this FF to derive
thermodynamic, structure, and transport properties of the mixtures of
1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4], and acetonitrile
(ACN) over the whole composition range. Three approaches to derive a force
field are formulated based on different treatments of the ion-ion and
ion-molecule Coulomb interactions using unit-charge, scaled-charge and
floating-charge approaches. The simulation results are justified with the help
of experimental data on specific density and shear viscosity for these
mixtures. We find that a phenomenological account (particularly, simple
scaled-charge model) of electronic polarization leads to the best-performing
model. Remarkably, its validity does not depend on the molar fraction of
[BMIM][BF4] in the mixture. The derived FF is so far the first molecular model
which is able to simulate all transport properties of the mixtures, comprising
RTIL and ACN, fully realistically.
