Multiple Free Energy Calculations from Single State Point Continuous Fractional Component Monte Carlo Simulation Using Umbrella Sampling

Journal Article (2020)
Author(s)

A. Rahbari (TU Delft - Engineering Thermodynamics)

R. Hens (TU Delft - Engineering Thermodynamics)

Othonas A. Moultos (TU Delft - Engineering Thermodynamics)

D. Dubbeldam (Universiteit van Amsterdam)

Thijs JH Vlugt (TU Delft - Engineering Thermodynamics)

Research Group
Engineering Thermodynamics
Copyright
© 2020 A. Rahbari, R. Hens, O. Moultos, D. Dubbeldam, T.J.H. Vlugt
DOI related publication
https://doi.org/10.1021/acs.jctc.9b01097
More Info
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Publication Year
2020
Language
English
Copyright
© 2020 A. Rahbari, R. Hens, O. Moultos, D. Dubbeldam, T.J.H. Vlugt
Research Group
Engineering Thermodynamics
Issue number
3
Volume number
16
Pages (from-to)
1757-1767
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Abstract

We introduce an alternative method to perform free energy calculations for mixtures at multiple temperatures and pressures from a single simulation, by combining umbrella sampling and the continuous fractional component Monte Carlo method. One can perform a simulation of a mixture at a certain pressure and temperature and accurately compute the chemical potential at other pressures and temperatures close to the simulation conditions. This method has the following advantages: (1) Accurate estimates of the chemical potential as a function of pressure and temperature are obtained from a single state simulation without additional postprocessing. This can potentially reduce the number of simulations of a system for free energy calculations for a specific temperature and/or pressure range. (2) Partial molar volumes and enthalpies are obtained directly from the estimated chemical potentials. We tested our method for a Lennard-Jones system, aqueous mixtures of methanol at T = 298 K and P = 1 bar, and a mixture of ammonia, nitrogen, and hydrogen at T = 573 K and P = 800 bar. For pure methanol (N = 410 molecules), we observed that the estimated chemical potentials from umbrella sampling are in excellent agreement with the reference values obtained from independent simulations, for ΔT = ±15 K and ΔP = 100 bar (with respect to the simulated system). For larger systems, this range becomes smaller because the relative fluctuations of energy and volume become smaller. Without sufficient overlap, the performance of the method will become poor especially for nonlinear variations of the chemical potential.