van der Waals density functional study of CO2 binding in zeolitic imidazolate frameworks

Abstract

The van der Waals density functional (vdW-DF) formalism is employed in a study of the binding energetics for CO2 in a set of five zeolitic imidazolate framework (ZIF) compounds. The ZIF structures investigated share the same RHO-type zeolite topology and metal atoms, but feature imidazolate linkers with different chemical functionalization. Three distinct binding sites are identified, for which the binding energies are found to show different dependencies on the functionalization of the linker molecules. The origin of the variations in the binding energies across the ZIF compounds is discussed through analyses of the binding geometries and charge-density distributions. A comparison of the vdW-DF results with those obtained by generalized-gradient-approximation calculations highlights the important contribution of the nonlocal correlation energy to the CO2 binding energies in these compounds.