Although of reasonable density, the ReaxFF crystal shows a larger bulk modulus by comparison with AIMD and experimental results. The bulk moduli and densities reported for the ab initio glasses do not contrast with the values computed for the crystal as clearly than with AIMD. The glass models which display higher K, represent states of considerably higher densities than the ab initio glass model and than the experimentally determined crystallographic density of ZIF-4 glasses, and are therefore not directly comparable. An alternative option is the use of the finite stress difference method, in which the MD simulations are performed in the constant-pressure (N, P, T ) ensemble at a given P , before measuring the volume V (P ). It is illustrated on Figure . This approach is more commonly used in conjunction with classical and reactive force fields. We evaluate the method using two possible variants, with an isotropic or a flexible cell (respective LAMMPS keywords iso and tri), as a previous work showed that this choice can impact the description of the glass.