title: Ab Initio Prediction of Adsorption Isotherms for Small Molecules in Metal-Organic Frameworks.
abstract: For CO and N2on Mg2+sites of the metal-organic framework CPO-27-Mg (Mg-MOF-74), ab initio calculations of Gibbs free energies of adsorption have been performed. Combined with the Bragg-Williams/Langmuir model and taking into account the experimental site availability (76.5%), we obtained adsorption isotherms in close agreement with those in experiment. The remaining deviations in the Gibbs free energy (about 1 kJ/mol) are significantly smaller than the "chemical accuracy" limit of about 4 kJ/mol. The presented approach uses (i) a DFT dispersion method (PBE+D2) to optimize the structure and to calculate anharmonic frequencies for vibrational partition functions and (ii) a "hybrid MP2:(PBE+D2)+ΔCCSD(T)" method to determine electronic energies. With the achieved accuracy (estimated uncertainty ±1.4 kJ/mol), the ab initio energies become useful benchmarks for assessing different DFT + dispersion methods (PBE+D2, B3LYP+D*, and vdW-D2), whereas the ab initio heats, entropies, and Gibbs free energies of adsorption are used to assess the reliability of experimental values derived from fitting isotherms or from variable-temperature IR studies.
authors.affiliation: Institut für Chemie, Humboldt-Universität zu Berlin , Unter den Linden 6, 10099 Berlin, Germany.
authors.forename: Arpan
authors.initials: A
authors.lastname: Kundu
authors.affiliation: Institut für Chemie, Humboldt-Universität zu Berlin , Unter den Linden 6, 10099 Berlin, Germany.
authors.forename: GiovanniMaria
authors.initials: G
authors.lastname: Piccini
authors.affiliation: Institut für Chemie, Humboldt-Universität zu Berlin , Unter den Linden 6, 10099 Berlin, Germany.|Institute of Chemistry, University of Tartu , Ravila 14 a, 50411 Tartu, Estonia.
authors.forename: Kaido
authors.initials: K
authors.lastname: Sillar
authors.affiliation: Institut für Chemie, Humboldt-Universität zu Berlin , Unter den Linden 6, 10099 Berlin, Germany.
authors.forename: Joachim
authors.initials: J
authors.lastname: Sauer