tensile test on Polymaide using fix deform

Dear Lammps-Users,

I want to simulate a tensile test on Polyamide 6.6. If I use the fix
deform command with an npt ensemble the
simulation box stretches in x-direction, but the molecule chains do not
move in that direction. Analyzing the output data, I noticed that the
pressure in x-direction doesnt increase either.

Furthermore, I get pressure fluctuations in all directions of about 10000
atm. At least I think the unit for pressure is atmosphere since I set the
the units to "real".

Actually I used almost the same code as they did in the tutorial


Is it possible that the initial configuration of the molecules or the force
field stop the polymer deforming? I want to simulate the crystal structure
of the polymer, so the the 16 chains I used are aligned to each other.
Then I reduced the Energy via minimization command and did a equilibrium
simulation similar to the one in the tutorial.

The script I used is attached to the mail, as is the equilibrium
simulations preceding the deformation and a movie file showing the
deformation process.

I would be very glad if someone could help me out here.

Thanks for your efforts.

Best regards


PA6_deform.avi (6.67 MB)

in.deformation.txt (4.36 KB)

in.equil.txt (4.55 KB)