Calculating Thermodynamic Properties of an Ionic Liquid with Monte Carlo Simulations with an Orthorhombic and a Cubic Simulation Box

In contrast to the common usage of cubic simulation boxes, in this work simulations of the ionic liquid 1-n-butyl-3-methyl-imidazolium hexafluorophosphate ([bmim][PF6]) were carried out in a dynamic orthorhombic simulation box over a temperature range from 313 to 373 K in a canonical harmonical simulation ensemble (NpT) with a united-atom potential based on quantum chemistry. The solubilities of the gases CO2, CO, H-2, O-2, C2H4, and H2O at infinite dilution were determined by means of the Widom test particle method; the results are compared with experimental data and simulation results obtained with a cubic simulation box. For gas potentials containing partial charges the results are in good agreement with the experimental data.