REGULAR ARTICLE Basis set effects on Cu(I) coordination in Cu-ZSM-5: a computational study Simone Morpurgo • Giuliano Moretti • Mario Bossa Received: 7 October 2011 / Accepted: 4 January 2012 / Published online: 28 February 2012 Ó Springer-Verlag 2012 Abstract DFT calculations on the coordination of Cu ? to the framework oxygen atoms of Al-substituted ZSM-5 were performed by using combinations of different basis sets in order to investigate the dependence of the results on the adopted computational level. With low-end basis sets, a large basis set superposition error (BSSE) favors the coordination of Cu ? to three to four oxygen atoms of the framework, only two of which belong to the AlO 4 tetra- hedron corresponding to the investigated T-site. More extended basis sets considerably lower the BSSE and favor the coordination of Cu ? to only two oxygen atoms of the AlO 4 tetrahedron. Upon interaction with NO, the Cu ? ion is always coordinated by two oxygen atoms of the AlO 4 tetrahedron, independently of the basis set adopted and of the coordination number before NO adsorption. The shift from three- to twofold coordination caused by the Cu ? –NO interaction requires a deformation energy that lowers the final adsorption energy. Such an effect is relevant with low- end basis sets, whereas it is substantially absent with more extended basis sets, which favor the twofold coordination of Cu ? even before NO adsorption. As a result, high-end basis sets increase the NO interaction energy with respect to that calculated by low-end basis sets, in agreement with experiments and suggesting a possible re-interpretation of the catalytic properties of the investigated sites. Provided suitable scale factors are employed, the N–O stretching frequencies of adsorbed nitrogen oxide calculated by suf- ficiently extended basis sets turned out in fair agreement with experimental findings. Keywords Zeolites Á Cu-ZSM-5 Á Nitrogen oxide Á DFT 1 Introduction Since its discovery by Iwamoto [1, 2], a huge number of studies was published on Cu-ZSM-5 as a catalyst for NO decomposition, due to its superior activity with respect to other zeolites and supported metal catalysts [3–6]. None- theless many points are still under discussion, mainly the nature of active site [7–25] and the reaction mechanism [26–33]. The major problem related to the structural char- acterization of Cu-ZSM-5, and zeolites in general, is to establish where the Si/Al substitution takes place and how metal cations are coordinated to substituted sites [34, 35]. This point is particularly important since the geometrical features of metal-framework coordination greatly influence the reactivity of the catalyst. Many commonly adopted experimental techniques can give useful information but very seldom they provide unequivocal answers. Theoretical calculations, when coupled to experiments, allow to investigate and to discuss many details that cannot be directly provided by experimental results. The main chal- lenge related to the application of quantum mechanical calculations is to find a compromise between accuracy and computational costs, taking into account that zeolites are complex solids with large unit cells. The most simple and the most complex computational approaches are, respec- tively, quantum mechanical calculations on small and non- structure-specific cluster models [36–41], or the application of quantum–mechanical methods (mostly based on plane- waves DFT) to the full periodicity of the zeolite lattice [42–50]. Apart from the above two extreme cases, the most widely employed approaches are nowadays molecular orbital calculations which treat only a portion of the S. Morpurgo (&) Á G. Moretti Á M. Bossa Dipartimento di Chimica, Universita ` degli Studi di Roma ‘‘La Sapienza’’, P.le Aldo Moro 5, 00185 Rome, Italy e-mail: simone.morpurgo@uniroma1.it 123 Theor Chem Acc (2012) 131:1180 DOI 10.1007/s00214-012-1180-4