Optimized Mie Potentials for Phase Equilibria: Application to Branched Alkanes

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.