(685g) Reaction Ensemble Monte Carlo: Applications to Ionic Liquids

Reaction ensemble Monte Carlo (RxMC) has been successfully used to study equilibrium compositions in many non-ideal environments, e.g. in nanopores or at high temperatures and pressures. In classical simulations, a reaction move is accomplished by deleting reactant molecules and inserting product molecules. Random insertions and deletions in condensed phases are rarely accepted. In simple liquids, this problem can be overcome using continuous fractional component (CFC) Monte Carlo with Wang-Landau (WL) biasing. But in ionic liquids, the extremely low vapor pressure and heterogeneous nanostructure cause even CFC-WL to fail. We present a simple adaptation of the original reaction move to align both the position and orientation of inserted product molecules to the deleted reactant molecules. We discuss applications to absorption of CO₂ in the ionic liquid triethyloctylphosphonium 2-cyanopyrrolide, [P2228][cnp] and the dissociation of the acid-base pair acetic acid and N-methylpyrrolidine.