Uncertainty quantification confirms unreliable extrapolation toward high pressures for united- atom Mie lambda-6 force field

Published

September 21, 2018

Author(s)

Richard A. Messerly, Michael R. Shirts, Andrei F. Kazakov

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 lambda-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 lambda-6 potential parameterized with VLE properties. Bayesian inference confirms that no feasible combination of nonbonded parameters (epsilon, sigma, and lambda) 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.

Citation

The Journal of Chemical Physics

Pub Type

Journals

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Keywords

Transferability, Molecular Dynamics, Molecular Simulation, Monte Carlo, Markov Chain, Bayesian Inference

Citation

Messerly, R. , Shirts, M. and Kazakov, A. (2018), Uncertainty quantification confirms unreliable extrapolation toward high pressures for united- atom Mie lambda-6 force field, The Journal of Chemical Physics, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=925699 (Accessed April 18, 2024)