you can use fix wall command with shrink-wrapped (s) boundary conditions.

Thank you for your reply. Can you tell me how to use fix wall command? There are a number of different fixes associated with wall in the documentation.

I think fix wall/lj93 would do the job. but i think, you can not move both upper and lower walls at the same with this fix.

an alternative method is to use groups of atoms in upper and lower regions to act like rigid walls. for this purpose you can use the following code.

boundary s p p

region lower block INF xmin INF INF INF INF

region upper block xmax INF INF INF INF INF

group lower region lower

group upper region upper

velocity lower set -10 0 0 units box

fix 2 lower setforce 0 0 0

velocity lower set 10 0 0 units box

fix 3 upper setforce 0 0 0

group middle subtract all upper lower

...

Thanks so much for your kind help.

Hello,

If I want to get 1e-3/ps strain rate what velocity should I use in the velocity command? Thanks.

The following three lines apply a strain rate of 1e-3/ps to a model (along the y-direction) in LAMMPS:

1. variable srate equal 1.0e9

2. variable   srate1 equal "v_srate / 1.0e12

3. fix        4 all deform 1 y erate ${srate1} units box remap x

The full code and other information are available here: https://www.linkedin.com/pulse/how-perform-uniaxial-tensile-tests-graphene-sample-lammps-dewapriya/

Thanks Nuwan Dewapriya for your clear instructions. It's late tho. I don't know how I missed your answer. By the way, your works on graphene are amazing. Thanks again.

Nuwan Dewapriya ur suggested deform command is showing incorrect in cmd

Dear Tousif Ahmed ,

Did you succed to apply uniaxial deformation with the vaccum region using LAMMPS? I have the same problem.

Hello, everyone

I am a beginner in LAMPS and want to find the mechanical properties (deformation, stress-strain, and heating and cooling effect) of CuNiFe alloy.

so help me, how to calculate in LAMMAS