Generation of thermodynamic data for organic liquid mixtures from molecular simulations

Abstract

Fluctuation solution theory (FST) is employed to analyze results of molecular dynamics (MD) simulations of liquid mixtures. The objective is to generate parameters for macroscopic thermodynamic property models. Two benchmark systems, benzene–methyl acetate at 303.15 K and benzene–ethanol at 298.15 K, are used. MD simulations are performed in the isobaric–isothermal ensemble (NPT) at the respective temperatures and at a pressure of 1 atm. We use the CHARMM27 force field at different mixing ratios. We sample positions to determine the binary (between the centers-of-mass of molecules of a pair) radial distribution functions (RDFs). The RDFs are integrated to give the total correlation function integrals (TCFIs). Errors in TCFIs due to uncertainties in RDFs from simulation have been overcome by introducing a simple expression to reproduce the indirect interactions allowing reliable extrapolation to infinite distances. We compare the results of our computations with measured data on both systems studied. The results for activity coefficients agree to within experimental uncertainty.

Keywords:

• Fluctuation solution theory
• Activity coefficients
• Organic solutions
• Liquids
• All-atom force field
• NPT simulations

Acknowledgements

The authors gratefully acknowledge access to the Danish Center for Scientific Computing at the University of Southern Denmark, Odense, Denmark. S. Christensen acknowledges financial support from DANISCO A/S. G. H. Peters acknowledges financial support from the Danish National Research Foundation via a grant to MEMPHYS.