Theoretical assessment of the elastic constants and hydrogen storage capacity of some metal-organic framework materials
Journal of Chemical Physics
Metal-organic frameworks ͑MOFs͒ are promising materials for applications such as separation, catalysis, and gas storage. A key indicator of their structural stability is the shear modulus. By density functional theory calculations in a 106-atom supercell, under the local density approximation, we find c 11 = 29.2 GPa and c 12 = 13.1 GPa for Zn-based MOF 5. However, we find c 44 of MOF-5 to be exceedingly small, only 1.4 GPa at T = 0 K. The binding energy E ads of a single hydrogen molecule in
... rogen molecule in MOF-5 is evaluated using the same setup. We find it to be −0.069 to − 0.086 eV/ H 2 near the benzene linker and −0.106 to − 0.160 eV/ H 2 near the Zn 4 O tetrahedra. Substitutions of chlorine and hydroxyl in the benzene linker have negligible effect on the physisorption energies. Pentacoordinated copper ͑and aluminum͒ in a framework structure similar to MOF-2 gives E ads Ϸ −0.291 eV/ H 2 ͑and −0.230 eV/ H 2 ͒, and substitution of nitrogen in benzene ͑pyrazine͒ further enhances E ads near the organic linker to −0.16 eV/ H 2 , according to density functional theory with local density approximation.