[lammps-users] Apply an external pressure

Dear Steve,

I have used the Lammps in the simulation of the water into the CNT, and the model is constructed by the following components from top to down:

A piston sits on the top of a reservoir
A reservoir of water
Below the reservoir there is a long CNT

In the simulation, I want to apply a constant pressure on the water through the piston, and at the same time, move the piston by applying a constant velocity. It is easy for me to apply a constant velocity on the piston. I have tried several ways to apply a constant pressure on the piston, and it did not work. Is it possible to apply an external pressure on the water through the piston and keep it constant during the movement of the piston? Could you please give me some suggestions? Thank you very much for your help.

Baoxing Xu

Dear Steve,

I have used the Lammps in the simulation of the water into the CNT,
and the model is constructed by the following components from top to down:

A piston sits on the top of a reservoir
A reservoir of water
Below the reservoir there is a long CNT

In the simulation, I want to apply a constant pressure on the water through
the piston, and at the same time, move the piston by applying a
constant velocity. It is easy for me to apply a constant velocity on
the piston. I have tried several ways to apply a constant pressure on the
piston, and it did not work. Is it possible to apply an external pressure

please note that "it does not work" is a very bad description of a problem,
and generally an expression that should be avoided in a scientific context.
please explain what you did, what you expected to get and what you
found instead.

i would expect that the scenario you are describing would be doable
by using a constant force on the piston. the pressure will fluctuate, but
that is normal, particularly with a small number of particles. are real
"constant" pressure only exists in macroscopic environments (same
as for temperature) that are and stay in equilibrium.

cheers,
   axel.