The phenomenon of NTE in MOFs and related network materials is generally a result of phonon vibrations. Specifically, NTE results from the often complex combination of transverse vibrational modes throughout the periodic lattice and rigid unit modes. To confirm the presence of transverse phonon modes in the investigated MOFs, we computed the normal modes of vibration and subsequently generated total phonon density of states for MOF-399, DUT-60 and NU-110, the three best performing frameworks, using finite-displacements and the harmonic approximation. The total phonon density of states are displayed in Fig- .