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This work reports predictions from molecular simulation results for the solubility of the single gases carbon dioxide, carbon monoxide, and hydrogen in the ionic liquid 1-N-butyl-3-methyl-imidazolium hexafluorophosphate ([bmim][PF6]) at temperatures from 293 to 393 K and at pressures up to 9 MPa. The predictions are achieved by Gibbs ensemble Monte Carlo simulations at constant pressure and temperature (NpT-GEMC). The intermolecular forces are approximated by effective pair potentials for the pure gases and by a quantum-chemistry-based pair potential for [bmim][PF6]. The interactions between unlike groups are described using common mixing rules without any adjustable binary interaction parameter. The simulation results for the solubility of hydrogen agree within their statistical uncertainty with experimental data, whereas the results for carbon monoxide and carbon dioxide reveal somewhat larger deviations.

A method for calculating the pressure in molecular simulations that does not require calculation of the virial is proposed, building on earlier work by [R. Eppenga and D. Frenkel, Mol. Phys. 52, 1303 (1984)]. The method requires ‘‘test’’ volume changes and it is particularly efficient for ensembles demanding volume fluctuations, such as the Gibbs ensemble. The method is validated by calculating the pressure in Gibbs ensemble simulations for monoatomic and polyatomic fluids.

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