Rapid screening of gas solubility in ionic liquids using biased particle insertions with pre-sampled liquid trajectories

ABSTRACT

We present an efficient, general-purpose variant of the Widom test particle insertion method for computing chemical potentials of gaseous solutes in fluids or porous solids. The method is implemented in the Monte Carlo molecular simulation engine Cassandra, but receiving phase configurations are independent of this process and may be pre-sampled by other molecular simulation engines such as molecular dynamics codes. Efficiency enhancements present in this method include configurational biasing and accelerated atomic overlap detection. When applied to the estimation of Henry's law constants of atomistic difluoromethane and pentafluoroethane in ionic liquids, the accelerated overlap detection results in a speedup of more than an order of magnitude compared to conventional methods without sacrificing accuracy. We found good agreement between this method and Hamiltonian replica exchange (HREX) for Henry's law constant and absorption isotherm estimation. This embarrassingly parallel method is especially well suited for screening Henry's law constants of many small gases in the same solvents, since a liquid trajectory can be reused for as many solutes as desired.

KEYWORDS:

• Free energy
• cell list
• ionic liquids
• Widom insertions
• hydrofluorocarbons

Acknowledgments

Computing resources were provided by the Center for Research Computing (CRC) at the University of Notre Dame. We thank Dr. Ryan DeFever for providing us with HREX results.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Associated content

Example input files for LAMMPS and Cassandra simulations like those performed for this work are provided at https://github.com/MaginnGroup/widom_IL_examples.

The repository for Cassandra can be found at https://github.com/MaginnGroup/Cassandra.

Additional information

Funding

The authors are thankful for the financial support from the National Science Foundation via grant EFRI DChem: Next-generation Low Global Warming Refrigerants, Award No. 2029354.