I am trying to run nemd shock simulation on water through momentum mirror technique with tip4p flexible potential. Errors originated due to change of periodic boundary to fixed condition along shock propagation direction (here along Z). First error was tip4p hydrogen missing which I sorted out with help of pbc wrap command in VMD as suggested by Axel Sir. The molecules with fragments on other side were identified and slightly shifted in order to occupy completely inside box. This does not affect the density or initial temp. of 300K. Next error was regarding the use of kspace style pppm/tip4p which is only applicable for periodic boundary conditions. This was sorted with help of kspace_modify slab command applicable for p p f boundary condition. Further errors were Angle atoms 2576 2577 2578 missing on proc 19. I was introducing a gap of 2 nm between molecules and walls of reflection in order to prevent from unsteady shock. As the gap was removed, angle atoms missing error was sorted out. I don’t know the reason behind it. It was just a trial result. Now I am facing same type of error of “bond missing atoms on proc 0 at step 65” along with “out of range atoms-cannot compute pppm”. I tried with different timestep but result is same. Also this can’t be due to multiprocessor simulation as I had tried it with 1 cpu also. I had followed many Lammps threads regarding above mentioned errors.