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Hi Diego,
I can recommend to use Mezeiâs MMC code (http://inka.mssm.edu/~mezei/mmc/). In GCMC,
the chemical potential, volume and temperature are constant and relative
pressure (i.e. the pressure of the vapour phase normalized by the pressure of
the saturated vapour) can be given by the actual chemical potential and the
chemical potential corresponding to the point of condensation. In order to get
adsorption isotherm (and find the point of condensation) you should run a series
of simulations varying the chemical potentials systematically (pay attention for
hysteresis in the case of microporous material). To do the math, all the
necessary formula can be found in Phys.Chem.Chem.Phys., 2010, 12,
4604â4616.
Good luck!
MilÃn
Hello Diego,
As a first approximation, you can assume the gas is
ideal. In this case, the activity / fugacity will be the same as the pressure
and you can use the standard ideal gas relation for the chemical potential. So
at this level of approximation, no addition simulation is
necessary.
If you are dealing with adsorption under high pressure,
low temperature conditions where the pressure of the gas deviates significantly
> from the idea gas prediction, additional calculations will be required to
calculate deviation from non-ideality. From these you can
then calculate
the fugacity and chemical potential. You would need a NPT
MC or MD
calculation to calculate the real gas density at the T and P of interest, and
> from this data, calculate the fugacity and from that the chemical potential.
This calculation would have to be repeated for each pressure of the isotherm
because the deviation from ideality depends on the
pressure and
temperature.
Hope this helps!
From: owner-chemistry+saman.alavi==nrc.ca*_*ccl.net [owner-chemistry+saman.alavi==nrc.ca*_*ccl.net] On Behalf Of DIEGOI GOMEZ darkego21##yahoo.com [owner-chemistry*_*ccl.net] Sent: November 15, 2011 1:41 PM To: Alavi, Saman Subject: CCL: GCMC isotherms Hello...
I am new
in MC simulations, therefore any answer at any level is welcome!!
I want to
perform GCMC simulations to compute an adsorption isotherm of a gas in a
microporous material employing a particular force field (FF) derived > from QM
calculations.
To perform
the simulations, I'm testing GULP and Towhee. (Any other suggestion for an open
source software would be nice!)
With GULP
you can perform a GCMC simulation easily. However, you need a value for the
chemical potential (at a given pressure) and here is my first question.
i.
ÂHow to
obtain efficiently and accurately the chemical potential value for a given
pressure to start the GCMC calculation?
In this regard, it is possible to
obtain the chemical potential from a 'NPT' MC simulation that I could
perform in Towhee. However I would
like to know if (and to skip the format of the FF for Towhee) :
ii.
ÂIt is
possible to perform a 'NPT' MC simulation with GULP?
Any
manual, reference, comment or suggestion is welcome!!
Thanks in
advance for any reply!
Diego
GÃmez
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