Increasing volume in NPT simulation

Dear Lammps developers and users,

I am trying to simulate a system of carbon material solvated with water.

In the process of NPT simulation with ‘fix npt’

I found that the z-dimension of the simulation box increases too much.

I would appreciate if I can get help in finding what is wrong.

I attach the input and data file along with a pdf file which shows

the final snapshot of the simulation trajectory.




in.lmp (2.03 KB) (1.1 MB)

snapshot.pdf (595 KB)

You can monitor both the Pzz component of the pressure
and the z box length in thermo output. Pzz is what is
driving z to increase or decrease. I imagine if you do
that you will see there is a strong positive Pzz that is

greater than your target pressure. Which means it

is what your model is asking NPT to do. You can also

look at the damping factors in the fix npt command and insure

they are appropriate to not induce oscillations or too-slow
or response.