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 pr=
essure and you can use the standard ideal gas relation for the chemical pot=
ential. So at this level of approximation,
no addition simulation is necessary.

If you are dealing with adsorption under high pr=
essure, low temperature conditions where the pressure of the gas deviates s=
ignificantly from the idea gas prediction, additional calculations will be =
required to calculate deviation from
non-ideality. From these you can then calculate the fugacity a=
nd chemical potential. You would need a NPT MC or MD calcu=
lation to calculate the real gas density at the T and P of intere=
st, and from this data, calculate the fugacity and from that
the chemical potential. This calculation would have to be repeated fo=
r each pressure of the isotherm because the deviation from ideality=
depends on the pressure and temperature.

Hope this helps!

Hel=
lo...

I a=
m new in MC simulations, therefore any answer at any level is welcome!!

I w=
ant to perform GCMC simulations to compute an adsorption isotherm of a gas =
in a microporous material employing a particular force field (FF) derived f=
rom QM calculations.

To =
perform the simulations, I'm testing GULP and Towhee. (Any other suggestion=
for an open source software would be nice!)

Wit=
h 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 quest=
ion.

i. =
=BFHow to obtain efficiently and accurately the chemical potential value fo=
r a given pressure to start the GCMC calculation?

In this regard, it is poss=
ible to obtain the chemical potential from a 'NPT' MC simulation that I cou=
ld perform in =
Towhee. However I would like to know if (and to skip
the format of the FF for Towhee) :

ii.=
=BFIt is possible to perform a 'NPT' MC simulation with GULP?

Any=
manual, reference, comment or suggestion is welcome!!

Tha=
nks in advance for any reply!

Die=
go G=F3mez