Phase coexistence and free energy calculations by Monte Carlo simulation
Abstract
Three new Monte Carlo algorithms for determining the conditions of phase coexistence are studied. Good results were obtained for methane/ethane and ethane/propane mixtures by calculating the free energy by integrating the configurational energy with respect to 1/kT from the temperature of interest to an infinite temperature reference state. Multi-cell sampling in the Gibbs ensemble, where the transition probabilities used to fluctuate the number of molecules in each phase were based on an average energy change rather than the instantaneous change caused by particular particle insertions and deletions, was successful for the Lennard-Jones fluid, but was ineffective with more complex molecules. The method of temperature perturbation was developed and applied to the square well fluid, the Lennard-Jones fluid, ethane, propane, n-butane, methanol and water. The method of temperature perturbation was also found to be effective at calculating the free energy near the critical point and in the unstable two phase region. Complete Helmholtz energy isotherms were found at several temperatures for each of the fluids studied, and the volumes of the spinodal and binodal states were found.
Degree
Ph.D.
Advisors
Greenkorn, Purdue University.
Subject Area
Chemical engineering|Chemistry
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