We then investigated the use of the (N, P, T ) ensemble with our two FF adaptations, again with both an isotropic and a flexible cell as done for ReaxFF (see Figure ). We see on the results presented in Table that no system reaches a state of unreasonably high density (unlike with a reactive force field). In particular, MOF-FF handles better the additional degree of freedom brought by the free shape of the cell than does ReaxFF, although a flexible cell still leads to a larger densification, particularly for the crystal. We note that both FF adaptations give similar average results, with still a significant variance over the different glass models. Finally, K values are consistent with the finite strain difference method, and the previously observed trends of K glass > K crystal and increasing K with respect to ρ 0 are found again.