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There exist 12 crystallographically distinct Al-sites in the ZSM-5 zeolite, associated with which there are various Na-sites. Understanding their locations, while being the key to the understanding of the catalytic properties of this material, remains a great challenge in both experiment and theory. We present here a theoretical survey of the Na(+) location along with the Al distribution in ZSM-5 by using hybrid methods, ONIOM (our Own N-layer Integrated molecular Orbital molecular Mechanics) as well as the newly developed extended ONIOM (XO) (Guo, W. P.; Wu, A. A.; Xu, X. Chem. Phys. Lett. 2010, 498, 203-208) method. The reliability and efficiency of different methods/models have been systematically tested. Using the T1 Al-site as an example, our calculations demonstrate that the high-level layers of ONIOM models have to include all rings around the [AlO(4)] tetrahedron to have reliable coordination structures and energetics of different Na-sites, while XO can provide reliable results with 60% savings of computational time as compared to that of ONIOM. Our XO calculations reveal that, in most Al-sites, Na(+) preferentially occupies the six-membered-ring sites, and the most favorable Al-sites along with the Na-sites are T8/M6, T10/Z6, and T4/Z6. Conversely, those Al-sites only surrounded by five-membered rings, such as T6 and T3, are predicted to be energetically unfavorable.National Natural Science Foundation of China[10774126, 20923004]; Ministry of Science and Technology[2007CB815206, 2011CB808504

Here we present a systematical investigation on the effect of high-level layer selection in our own N-layered integrated molecular orbital + molecular mechanics (ONIOM) method. We used the adsorption of Na+ in the M7 site of ZSM-5 as an instructive example. We embedded n tetrahedral sites (nT = 7, 19, 22, 33) for high-level layer into a low-level layer represented by 75T (denoted as nT@75T). Our calculations showed that 7T@75T behaved poorly in both structure optimization and interaction energy calculation. Hence only including the first coordination circle of the ion (i.e. 7T), as commonly used in literature, is not sufficiently good. However, for n = 19, both structure optimization and interaction energy calculation by ONIOM are in good agreement with the full 75T model calculation. Such a reliable ONIOM calculation needs only 1/10 to 1/5 computational time for each self-consistent field (SCF) iteration as compared to the full 75T model calculation, highlighting its pivotal role in zeolite simulation.National Natural Science Foundation of China [20525311, 20533030, 10774126]; Ministry of Science and Technology [2004CB719902, 2007CB815206

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