I’m using lammps to simulate clay layers in periodic npt condition. In my simulations, there are top, bottom and middle layers, and the middle one is smaller than the others; while the top and bottom layers fully covers the planar area of the box, the middle layer has discontinuity. I’ve constrained all layers to only move in the z direction by:
fix freeze layers setforce 0.0 0.0 NULL
Since the edge atoms of the middle layer had huge movements in the z direction duo to discontinuity, I used:
fix holdEdge edgeAtoms aveforce NULL NULL 0.0
to control the atomic movements, but the problem is that this work gives incorrect results for the box size in the z direction and causes less contraction of the box in that direction. I appreciate any idea to resolve this issue.