Dear lammps developers and users
Thank you for your help in my previous simulation. Now, I’m trying to simulate filtration of water through a CNT with moving walls acting like piston to apply pressure difference. Therefore, my boundary condition is p p s.
I’m using TIP4P water model, since the kpace pppm/tip4p style doesn’t compatible with the boundary, I’ve changed the pair style which is lj/cut/tip4p/long to lj/cut/tip4p/cut. Is there any other suggestion so I can keep using lj/cut/tip4p/long but with boundary condition p p s? I’ve tried slab, but it wasn’t work, I got the error “Incorrect boundaries with slab PPPM”.
For the wall, the moving wall is made of carbon graphene layer. There are two walls, one at the zlo boundary and the other is at the zhi. I saw that people use wall/lj instead reflecting wall, I wonder if we can set force (the force of the wall acting to the fluid) in wall/lj, because only lj potentials that set as args in wall/lj fix. The wall/piston fix is worth to try, but it only set the wall moving velocity.
Then, I tried to use set/force and ave/force fix to the wall since it is easier to measure pressure from the force than from the velocity. Is there any suggestions?
I’m using LAMMPS version 11 July 2013
Thank you,
Steven
Dear lammps developers and users
Thank you for your help in my previous simulation. Now, I'm trying to
simulate filtration of water through a CNT with moving walls acting like
piston to apply pressure difference. Therefore, my boundary condition is p p
s.
I'm using TIP4P water model, since the kpace pppm/tip4p style doesn't
compatible with the boundary, I've changed the pair style which is
lj/cut/tip4p/long to lj/cut/tip4p/cut. Is there any other suggestion so I
can keep using lj/cut/tip4p/long but with boundary condition p p s? I've
tried slab, but it wasn't work, I got the error "Incorrect boundaries with
slab PPPM".
i see two possible ways to allow using long-range electrostatics:
1) use fully periodic boundaries, but make your box large enough to
hold the water molecules that you push through your filter.
2) check out MSM. it doesn't use reciprocal space and thus doesn't
require periodicity.
For the wall, the moving wall is made of carbon graphene layer. There are
two walls, one at the zlo boundary and the other is at the zhi. I saw that
people use wall/lj instead reflecting wall, I wonder if we can set force
(the force of the wall acting to the fluid) in wall/lj, because only lj
potentials that set as args in wall/lj fix. The wall/piston fix is worth to
i don't understand what you are asking here.
axel.
Dear lammps developers and users
Thank you for your help in my previous simulation. Now, I'm trying to
simulate filtration of water through a CNT with moving walls acting like
piston to apply pressure difference. Therefore, my boundary condition is p
p s.
I'm using TIP4P water model, since the kpace pppm/tip4p style doesn't
compatible with the boundary, I've changed the pair style which
is lj/cut/tip4p/long to lj/cut/tip4p/cut. Is there any other suggestion so
I can keep using lj/cut/tip4p/long but with boundary condition p p s? I've
tried slab, but it wasn't work, I got the error "Incorrect boundaries with
slab PPPM".
For the wall, the moving wall is made of carbon graphene layer. There are
two walls, one at the zlo boundary and the other is at the zhi. I saw that
people use wall/lj instead reflecting wall, I wonder if we can set force
(the force of the wall acting to the fluid) in wall/lj, because only lj
potentials that set as args in wall/lj fix. The wall/piston fix is worth to
try, but it only set the wall moving velocity.
Fix wall/lj variants have the option to set reflective strength via setting
the epsilon parameter. Please see its doc page for more details.
For wall/piston, velocity is correlated with reflective strength.
Ray
Yes, we can set the reflective strength, but what I want is the force which applied to the wall to push the fluid. Therefore, I can set the pressure difference. I have tried ave/force before, but I wonder whether there is another better option.
Thank you
Steven
If you conduct a series of 2 or more tests with varying wall strength, you can obtain a correlation between strength and applied force (using fix ave/force to measure the force). Then you can set the strength to the desired value.
Ray
Thank you for the suggestion, but I’ve decided to try using ave/force to both walls. The new problem is both of the walls don’t move, they just stand still. The water molecules don’t move too, the whole simulation is not moving although there’s no error in the running progress.
I have set the velocity, pair style and force to the piston walls, but the result is the molecules are not moving.
I attach my input script and data file here.
Thank you,
Steven
Data-Water-Graphene.txt (303 KB)
Input-Script-WaGraph.txt (3.08 KB)
Maybe your aveforce for the wall is too small. Try with exceptional large values and see if they move.
Ray
Thank you for the suggestion, I’ve just tried to add even bigger force, but the result is still same. The whole simulation just stand still in their position. Even the water molecules which should be moving even without any force are not moving (just stand still like a statue).
Steven
You will have to debug your own input script, but you don’t seem to have time integration fixes (nve, nvt, etc) in your script. That may be why nothing is moving.
Ray