Another approach to obtain mechanical properties at a given temperature T is to evaluate them from the fluctuations of the unit cell in the constant-stress (N, σ, T ) ensemble. Unlike the previous finite difference methods which only yield one property at a time, this leads to the estimation of the entire tensor of second-order elastic constants C which in turns is linked to mechanical properties such as Young's modulus, shear modulus, and Poisson's ratio. This approach, already used for the ZIF-4 crystal with a classical force field, requires long equilibration times (∼ 5 -10 ns) and is out of reach of AIMD simulations, but proves tractable with MLPs. The bulk modulus can then also be computed from the fluctuations of the volume. We also note that these very long simulations also highlight the good stability of the models trained as part of this work, which is a known issue for MLPs in some cases. Starting from the initial systems for the finite strain difference method, we performed further (N, P, T ) simulations with a flexible cell (LAMMPS keyword tri), corresponding to the (N, σ, T ) ensemble required by the method, until convergence of the volume (see Figure ) and elastic constants (see Figure ). From the results shown in Table , we see that the values of K obtained from the elastic constants are consistent with the more robust volume fluctuations, as are the K and ρ 0 values.