Rigid body breaking

This is incorrect. If you remove the wall from the time integration fix, they will not move due to forces on them, but their forces on the polymer will still be included in the equations of motion on the polymers. The approach I suggest is also mentioned in the docs of fix rigid.

on top of that, applying two time integration fixes (both, fix move and fix rigid do time integration) to the same atoms is almost always and this case a definite error. LAMMPS must have printed a warning and these warnings need to be taken seriously unless you know for a fact, that they don’t apply your specific case.

axel.

That was very helpful .Thank you so much.