hi
To whom may it concern,
I have a question about the lammps software.
I’m going to simulate the separation of a mixed gases system with porous graphene sheet.
I’d like to set the pressure of the mixture gas at the one of the side of the graphene sheet in order to provide a pressure gradient along the porous graphene sheet. (the separator).
I do not know how to include the pressure value in the input file for this case study.
hi
To whom may it concern,
I have a question about the lammps software.
for starters, this is not at all a question about LAMMPS, it is a
question about designing a simulation and there is nothing about it
that is specific to LAMMPS.
I'm going to simulate the separation of a mixed gases system with porous
graphene sheet.
I'd like to set the pressure of the mixture gas at the one of the side of
the graphene sheet in order to provide a pressure gradient along the porous
graphene sheet. (the separator).
I do not know how to include the pressure value in the input file for this
case study.
you *cannot*. it doesn't make sense. please revert to your fundamental
training in thermodynamics of gases (if you haven't received that, it
is now high time to make up for it, or you will suffer badly and
embarrass your self immensely in the future).
first of all, you are likely to be tempted to use fix npt. don't. it
is not designed for your kind of system, but to sample a *bulk* NPT
ensemble (which your system most certainly isn't).
now you have to think about how to set up a suitable simulation, and
the way to do so is a "two piston"-like setup, where you can implement
the desired pressure gradient through a couple of impenetrable walls.
you can use a setup where you keep two box dimensions periodic and
unchanged while the third would be non-periodic. in order to couple
your system to an external pressure you can use fix aveforce on your
wall particles with a different value for each side. since pressure is
force per area, it is trivial to compute what force you need to impose
on each side.
this kind of setup is described in many fundamental thermodynamics
text books and thus i suggest you have a look at one of those to make
sure you get the right idea about how this *can* work (and why your
initial question makes no sense. you cannot "set" pressure, only
measure it).
axel.