In particular, the eigenvalues of the C i j matrix are required to be positive for the structure to be elastically stable. The maximum and minimum values of these eigenvalues indicate the most rigid and softest deformation mode. As we do not impose symmetry constraints, these are useful metrics in non-cubic crystals. Notably, increasing temperature was found to soften the stiffest deformation mode, however, it does not change the softest mode, displayed for each MOF in the ESI. For example, MOF-399 shows a 50 % decrease in the stiffest deformation mode (Figure ).