Periodic Density Functional Theory (PDFT) Predicting the Structure and Bonding Strength of Dehydrated Alkaline-Earth Metal Cation-Exchanged Chabazite Sieves (CHA-M)

Ion-exchanged chabazites have wide applications in industry. In this study, dehydrated Be2+, Mg2+, Ca2+, Sr2+, and Ba2+-exchanged chabazite sieves (CHA-M) were designed, which differ from some reported natural and hydrated chabazite mineral series. Their crystal structures and electronic properties were carefully predicted using the PDFT//PBE+TS/HI method. Each CHA-M deviates from the space group R-3M slightly. The calculated crystal volume of CHA-M was underestimated by up to −3.28% relative to the related chabazite mineral. The alkaline-earth metal cation (M2+) with the Bader charge of +1.67 ~ +1.72 e gradually moves to the center of the 8MR window of the CHA framework as the atomic number increases. The predicted HOBO-LUBO gap of CHA-M ranges from 3.74 to 5.33 eV. The alkaline-earth metal atom serves as the primary electron-accepting site in CHA-M. The M2+-[CHA]2− bond is assumed to have an −ICOHP value ranging from 0.327 to 4.005 eV and a BDE value ranging from 4.61 to 8.75 eV. Contrary to CHA-Mg, CHA-Be is likely to exhibit the highest HOBO-LUBO gap, the strongest bonding strength between M2+ and [CHA]2−, and the biggest absolute value of Fermi energy (i.e., −2.193 eV) among the five species. This study may help researchers to design new zeolites.