multiple use of fix GCMC

Hello, everyone.

Recently, I am studying how to use ¡®fix gcmc¡¯ of the lammps.

As described in the documentation page of fix gcmc command, I cannot use multiple times of fix gcmc command in a single input script.

My problem is how to set different fix settings in the mixture.

In the example file of gcmc run, there are only systems composed of one kind of molecule.

Specific cases are written below,

Hello, everyone.

Recently, I am studying how to use ‘fix gcmc’ of the lammps.

As described in the documentation page of fix gcmc command, I cannot use
multiple times of fix gcmc command in a single input script.

My problem is how to set different fix settings in the mixture.

In the example file of gcmc run, there are only systems composed of one kind
of molecule.

Specific cases are written below,

For example, if I want to know the adsorbed amount of adsorbates at 70kPa
CO2 and 30 kPa N2 in a MOF, how can I set partial pressure of each molecule
in a single use of fix gcmc command? (following is what I want to do)

fix mygcmc1 co2 gcmc 10 20 0 0 \{seed\} {temp1} \{mu\} {disp}
mol &

                co2mol tfac_insert ${tfac1} pressure 0.7 group co2 rigid
myrigidnvt1

fix mygcmc2 n2 gcmc 10 20 0 0 \{seed\} {temp1} \{mu\} {disp} mol
&

                n2mol tfac_insert ${tfac2} pressure 0.3 group n2 rigid
myrigidnvt2

In addition, if I want to use different fix settings with same partial
pressure, e.g. one is using fix rigid/small/nvt, and the othere is using fix
nvt. In my condition, I assumed CH4 as an atom and CO2 as the rigid body,
but rigid body cannot be applied to monatomic molecule. In this case, how
can I apply ‘rigid’ keyword only for CO2. (following is what I want to do)

fix mygcmc1 co2 gcmc 10 20 0 0 \{seed\} {temp1} \{mu\} {disp}
mol co2mol tfac_insert ${tfac1} pressure 0.5 group co2 rigid myrigidnvt

fix mygcmc2 ch4 gcmc 10 20 0 0 \{seed\} {temp2} \{mu\} {disp}
pressure 0.5 group ch4

Thank you for sharing your time to read this mail.

why use fix gcmc for this at all? why not prepare a sufficiently large
reservoir of a mixture of the molecules of interest in the desired
proportions?
if the reservoir is large enough, it should make the error resulting
from absorbed molecules smaller than the error coming from fix gcmc.
you can have separate time integration for point particles and rigid
particles and also do separate thermalization.

axel.