A transferable united-atom (UA) force field based on Mie potentials is presented for branched alkanes. The performance of the optimized Mie potential parameters is assessed for 32 branched isomers of butane, pentane, hexane, heptane, and octane using grand canonical histogram-reweighting Monte Carlo simulations. For each compound, vapor−liquid-coexistence curves, vapor pressures, heats of vaporization, critical properties, and normal boiling points are predicted and compared to experiment. Experimental saturated liquid densities and critical temperatures are reproduced with a median absolute average error of 0.6%, while vapor pressures are reproduced with a median absolute average error of 2.2%. Calculations performed with the TraPPE and NERD force fields produce median absolute average errors for saturated liquid densities and vapor pressures of 1.3−1.8% and 14.3−23.5%, respectively. Binary phase diagrams predicted by the Mie potentials for argon+neopentane, methane+neopentane, and ethane+isobutane are in close agreement with experiment.

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Transferrable force fields, based on n-6 Mie potentials, are presented for noble gases. By tuning the repulsive exponent, ni, it is possible to simultaneously reproduce experimental saturated liquid densities and vapor pressures with high accuracy, from the normal boiling point to the critical point. Vapor-liquid coexistence curves for pure fluids are calculated using histogram reweighting Monte Carlo simulations in the grand canonical ensemble. For all noble gases, saturated liquid densities and vapor pressures are reproduced to within 1% and 4% of experiment, respectively. Radial distribution functions, extracted from NVT and NPT Monte Carlo simulations, are in similarly excellent agreement with experimental data. The transferability of the optimized force fields is assessed through calculations of binary mixture vapor-liquid equilibria. These mixtures include argon + krypton, krypton + xenon, methane + krypton, methane + xenon, krypton + ethane, and xenon + ethane. For all mixtures, excellent agreement with experiment is achieved without the introduction of any binary interaction parameters or multi-body interactions.

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