Another option to avoid this undesired densification may consist in staying in the constantvolume (N, V, T ) ensemble, similarly to what was done in the ab initio works. For example, pressure equilibration can be achieved by successive slow deformation of the cell until zero pressure is reached. When we performed this procedure in the case of the ZIF-4 crystal, it leads to a density of 1.26 g cm , not far from the experimental crystal density. However, although this approach could fix the troublesome densification, we end up losing all the benefits of the (N, P, T ) ensemble that every ReaxFF work published so far was interested in.