The importance of charge-quadrupole interactions for H2 adsorption and diffusion in CuBTC

We have assessed the effects of charge-quadrupole interactions (CQIs) between the framework atoms of copper(II) benzene-1,3,5-tricarboxylate (CuBTC) and adsorbed H2 molecules on equilibrium adsorption properties and self- and transport diffusivities. We have also compared charges computed from periodic density functional theory (DFT) on the fully periodic CuBTC structure with charges derived from DFT calculations on cluster models of CuBTC. Our results indicate that carboxylate group atom charges computed from plane wave periodic DFT with the Bader charge analysis formalism are not consistent with the charges computed from the ChelpG method from Gaussian-based DFT cluster calculations. The charges derived from Bader analysis seem to be too large. Adsorption isotherms computed from Monte Carlo simulations and diffusivities computed from molecular dynamics simulations indicate that CQIs have a substantial impact on equilibrium and transport properties of H2 adsorbed in CuBTC at 77K. Conversely, both adsorption isotherms and diffusivities were shown to be essentially unaffected by CQIs at 298K.