The defects can naturally exist or be artificially designed in metal−organic frameworks (MOFs), which could significantly affect their mechanical properties. In this paper, the elastic properties of HKUST-1 with randomly distributed missing linker defects are investigated by reactive molecular dynamics simulations together with the strain-fluctuation method. Although all elastic constants of HKUST-1 are found to reduce due to the linker missing, the cubic symmetry is retained in the defective HKUST-1, indicating that the simplified Born stability criterion is still applicable in determining its mechanical stability. On the basis of the simplified Born stability criterion together with direct compression simulations, the critical pressure of instability of HKUST-1 with randomly distributed defects is found to almost linearly decrease as the defect concentration grows. The mechanical instability is similarly attributed to the compression mode in both pristine and defective HKUST-1. Moreover, the direct compression simulations indicate an obvious intermediate transition process existing during the structural collapse of the defective HKUST-1, which is absent in its pristine counterpart. Overall, this work is expected to provide a more precise understanding of the mechanical properties of realistic MOFs.

Metal–organic frameworks (MOFs) are a family of materials that have high porosity and structural tunability and hold great potential in various applications, many of which require a proper understanding of the thermal transport properties. Molecular dynamics (MD) simulations play an important role in characterizing the thermal transport properties of various materials. However, due to the complexity of the structures, it is difficult to construct accurate empirical interatomic potentials for reliable MD simulations of MOFs. To this end, we develop a set of accurate yet highly efficient machine-learned potentials for three typical MOFs, including MOF-5, HKUST-1, and ZIF-8, using the neuroevolution potential approach as implemented in the GPUMD package, and perform extensive MD simulations to study thermal transport in the three MOFs. Although the lattice thermal conductivity values of the three MOFs are all predicted to be smaller than 1 W/(m K) at room temperature, the phonon mean free paths (MFPs) are found to reach the sub-micrometer scale in the low-frequency region. As a consequence, the apparent thermal conductivity only converges to the diffusive limit for micrometer single crystals, which means that the thermal conductivity is heavily reduced in nanocrystalline MOFs. The sub-micrometer phonon MFPs are also found to be correlated with a moderate temperature dependence of thermal conductivity between those in typical crystalline and amorphous materials. Both the large phonon MFPs and the moderate temperature dependence of thermal conductivity fundamentally change our understanding of thermal transport in MOFs.