The performance of the ONIOM (Our-own-N-layered Integrated molecular Orbital + molecular Mechanics) approach utilizing 10 combinations
of two-layer ONIOM2 schemes has been tested for various sizes of faujasite clusters containing up to 84T tetrahedral atoms and
the complexes they form with ethylene, benzene, and ethylbenzene molecules. Interaction energies of the adsorbates with a 3T bare quantum
cluster are calculated to be −8.14, −7.48, and −7.76 kcal/mol at B3LYP/6-31G(d,p) level of theory, respectively. The long-range effects
of the extended structure of zeolite were found to differentiate the stability of adsorption complexes that cannot be drawn from the typical
3T quantum cluster. The interaction energies of ethylene, benzene, and ethylbenzene molecules on the more realistic cluster, 84T, using
ONIOM2(B3LYP/6-311++G(d,p):UFF) scheme are predicted to be −8.75, −15.17, and −21.08 kcal/mol, respectively, which compare
well with the experimental estimates of −9.1, −15.3, and −19.6 kcal/mol, respectively. This finding clearly demonstrates that the interaction
between adsorbate and acidic zeolites does not depend only on the Brønsted group center but also on the lattice framework surrounding
the adsorption site. The results obtained in this study suggest that the ONIOM approach, when carefully calibrated, is a computationally
efficient and accurate method for studying adsorption of aromatics on zeolites.
2003 Elsevier Inc. All rights reserved.