Abstract
Molecular simulation results at extreme temperatures and pressures can supplement experimental data when developing fundamental equations of state. Since most force fields are optimized to agree with vapor-liquid equilibria (VLE) properties, however, the reliability of the molecular simulation results depends on the validity/transferability of the force field at higher temperatures and pressures. As demonstrated in this study, although state-of-the-art united-atom Mie λ-6 potentials for normal and branched alkanes provide accurate estimates for VLE, they tend to over-predict pressures for dense supercritical fluids and compressed liquids. The physical explanation for this observation is that the repulsive barrier is too steep for the "optimal" united-atom Mie λ-6 potential parameterized with VLE properties. Bayesian inference confirms that no feasible combination of non-bonded parameters (I, σ, and λ) is capable of simultaneously predicting saturated vapor pressures, saturated liquid densities, and pressures at high temperatures and densities. This conclusion has both practical and theoretical ramifications, as more realistic non-bonded potentials may be required for accurate extrapolation to high pressures of industrial interest.
Original language | English |
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Article number | 114109 |
Journal | Journal of Chemical Physics |
Volume | 149 |
Issue number | 11 |
DOIs | |
State | Published - Sep 21 2018 |
Externally published | Yes |
Funding
This research was performed while Richard A. Messerly held a National Research Council (NRC) Postdoctoral Research Associateship at NIST. Michael R. Shirts acknowledges support from the National Science Foundation (NSF) Grant No. CHE-1738975.
Funders | Funder number |
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National Science Foundation | 1738975 |
National Science Foundation |