Elastic analysis of ZIF-8 and ZIF-8 filled with hydrogen molecules by density functional theory

Understanding the mechanical properties of MOFs is important in many real applications. This study compared the mechanical properties (elastic constants, Poisson's ratio, Young's modulus, shear modulus, and bulk modulus) and analyzed the elastic anisotropy of both ZIF-8 and ZIF-8 filled with hydrogen molecules. The adsorption of hydrogen molecules inside the ZIF-8 framework is thermodynamically favorable with minimum potential energy. ZIF-8 with elastic anisotropy becomes isotropy once it is filled with 35 hydrogen molecules. ZIF-8 filled with hydrogen molecules is more difficult to be compressed, more resistant to attempted shearing, and transmits the shear energy more quickly than the empty ZIF-8 framework. Our findings provide insights into the functionality of the elastic constants in determining the structural stability of MOF materials and also open a possible way to load hydrogen molecules inside the ZIF-8 framework.