Theoretical Chemistry Accounts

, Volume 99, Issue 5, pp 347–350

Calculating Gibbs free energies of transfer from Gibbs ensemble Monte Carlo simulations

  • Marcus G. Martin
  • J. Ilja Siepmann

DOI: 10.1007/s002140050345

Cite this article as:
Martin, M. & Siepmann, J. Theor Chem Acc (1998) 99: 347. doi:10.1007/s002140050345


The partitioning of the ternary systems n-pentane/n-heptane/(helium or argon) at ambient conditions is investigated using configurational-bias Monte Carlo simulations in the Gibbs ensemble. The results demonstrate that this approach yields very precise partition constants and free energies of transfer. Simulations are carried out to study the dependence of the n-pentane partitioning with respect to the carrier gas, the system size, and the overall solute concentrations. None of the changes of variables, within the ranges used here, has a significant effect on the alkane partitioning. However, chemical potentials calculated via Widom's ghost particle insertions show a strong number dependence for phases containing relatively few molecules of a given type. This problem originates from the fact that the chemical potential is calculated for a concentration of real particles plus one ghost particle that is systematically larger than the equilibrium concentration. A simple correction term is suggested to account for this problem.

Key words: Alkane-vapor partitioningPhase equilibriaFree energies

Copyright information

© Springer-Verlag Berlin Heidelberg 1998

Authors and Affiliations

  • Marcus G. Martin
    • 1
  • J. Ilja Siepmann
    • 1
  1. 1.Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, MN 55455-0431, USAUS