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     COLLOQUIUM OF THE COMPUTATIONAL MATERIALS SCIENCE CENTER
   AND THE SCHOOL OF PHYSICS, ASTRONOMY AND COMPUTATIONAL SCIENCES
                       (CSI 898-Sec 001)
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      Use of transition matrix Monte Carlo simulation to study 
    metastability and phase transitions in gas adsorption processes

                            Daniel W. Siderius
    National Institute of Standards and Technology, Gaithersburg, MD

In light gas adsorption in porous materials, an understanding of the key
features of the adsorption isotherm and any engineering exploitation of those
features is often reliant on identification of the stable and metastable parts
of the phase diagram. In simple Monte Carlo simulations, such as those in the
grand canonical ensemble with normal Boltzmann sampling, it is difficult to
probe far into the metastable region;  more sophisticated techniques are
necessary to examine these regions of the phase diagram.

Recently, the Transition Matrix Monte Carlo (TMMC) technique has come to
prominence as a method for simulating gases and liquids and directly
identifying phase equilibria for the simulated fluid. When used in the grand
canonical ensemble, TMMC differs from normal Monte Carlo simulation in that
its aim is to generate the macrostate probability distribution instead of
directly compute ensemble average properties. From this probability
distribution, one can compute properties such as total density, pressure, and
the grand free energy and also identify stable and metastable states. In
combined with histogram reweighting, TMMC yields an entire density-pressure
isotherm from simulation of a single pressure-temperature state point.

We apply TMMC to light gas adsorption in porous materials such as graphitic
carbon to demonstrate the usefulness of the technique for the computation of
adsorption properties of a fluid confined in a porous material. Moreover, we
show that TMMC yields other insightful information about adsorption processes
not available via experiment or other simulation techniques. Overall, we aim
to introduce TMMC as a useful tool for studying fluid behavior in porous
materials.

                     Monday, October 24, 2011
                               4:30 pm
                    Room 301, Research I, Fairfax Campus

Refreshments will be served at 4:15 PM.
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Find the schedule at http://cmasc.gmu.edu/seminar/schedule.html