how can I add moving periodic boundaries

Hi all

I am planning to test the strength of one polymer chain, I only want to simulate one section of this polymer chain. I want to achieve it by applying the moving periodic boundaries along the pulling direction, as shown in figure below:
figure.png
The dashed lines represent the boundary of the simulation box, the arrow represent the force exerted on the atoms and the moving direction of the left and right boundary. The shadowed region means virtual, namely in this figure, the first atom only has the right side in the simulation box, the last atom only has the left side in the simulation box.

Another problem is that, you can see there are two atoms on the moving periodic boundaries, I am not sure whether this is doable.

Can any one tell me which command can achieve it? I would really appreciate your kindly and timely help.

Best regards

Hi all
I am planning to test the strength of one polymer chain, I only want to
simulate one section of this polymer chain. I want to achieve it by
applying the moving periodic boundaries along the pulling direction, as
shown in figure below:
!figure.png|453x144
The dashed lines represent the boundary of the simulation box, the arrow
represent the force exerted on the atoms and the moving direction of the
left and right boundary. The shadowed region means virtual, namely in this
figure, the first atom only has the right side in the simulation box, the
last atom only has the left side in the simulation box.

that is not a quite correct description. with periodic boundaries the first
and the last atom are the *same* atom.

Another problem is that, you can see there are two atoms on the moving
periodic boundaries, I am not sure whether this is doable.

yes, it should be doable. you need to take out one of the two atoms on the
boundary and make sure there is a bond that connects the chain across the
periodic boundary. LAMMPS will print a warning, but that can be safely
ignored in this case. the stretching can then be done via fix deform.

axel.