Comparison of embedded cluster models to study zeolite catalysis: Proton transfer reactions in acidic chabazite

Molecular Modeling of Interactions in Zeolites: An Ab Initio Embedded Cluster Study of NH3 Adsorption in Chabazite

“…The potential energy scans were generated by varying the N 11 -O 5 distance with NH 3 and NH 4 + principal axes directed along the O 5 -H 10 bond (see Figure 2). Figure 3 displays the potential energy curves for NH 3 and NH 4 + adsorption, calculated by different embedded cluster models (i.e., the present model and those from Pisani and Birkenheuer, 16 Teunissen et al, 18 and Greatbanks et al 24 ) as well as the periodic HF 35 and bare cluster methods. All embedded cluster methods predict that NH 3 binds to the acidic site more tightly than the bare cluster results (ranging from 2 kJ/mol for Teunissen et al's method to 25 kJ/mol for EM-BED93).…”

“…Second, we attempt to validate our model for the study of adsorbate/zeolite interactions by reproducing potential energy sections for head-on adsorption of NH 3 and NH 4 + at a chabazite Brønsted site, for comparison with previously reported embedded, periodic, and bare cluster results. 16,18,24 Third, we address the importance of the choice of environmental embedding charges by repeating these potential energy section calculations using three different sets of environmental embedding charges. Last, we look at the importance of structural relaxation by optimizing our embedded cluster.…”

Comparison of a combined quantum mechanics/interatomic potential function approach with its periodic quantum-mechanical limit: Proton siting and ammonia adsorption in zeolite chabazite

“…A paper has been overlooked 48 which compares the periodic STO-3G calculations 21 with a cluster model embedded in an array of potential derived point charges. 46 The conclusion is reached that this simple scheme shows better agreement with the periodic calculation than the more sophisticated embedding scheme used in Ref.…”

Computer simulation of zeolite structure and reactivity using embedded cluster methods

“…Furthermore, when compared to full periodic results, indications are that our simpler description is competitive with more sophisticated embedding techniques. 18 Although these charges which are derived from such a Ðtting technique, do reÑect the periodic nature of the lattice they need not be atom centred, and the individual values have no physical signiÐcance. Indeed, even if they are atom centred, atoms of the same type will have di †erent formal charges associated with them, depending upon the actual cluster chosen in the Ðtting procedure.…”