First Hybrid Embedding Scheme for Polar Covalent Materials Using an Extended Border Region To Minimize Boundary Effects on the Quantum Region.

Abstract

We present an improved scheme for constructing the border region within a hybrid quantum mechanics/molecular mechanics (QM/MM) embedded cluster approach for zeolites and covalent oxides that ensures proper modeling of adsorption complexes with QM regions of moderate size. The procedure employs a flexible orbital basis set on monovalent oxygen pseudoatoms at the boundary of the QM cluster and introduces a pseudopotential description without explicit representation of valence electrons for their immediate Si neighbors in the MM region. This novel QM/MM border scheme, implemented in the elastic polarizable environment method for polar covalent materials (covEPE), provides an accurate description of the local structure of zeolites and other silica based materials. We assessed the performance of the novel border scheme by comparing calculated and experimental results for structures, vibrational frequencies, and binding energies of CO adsorption complexes at bridging OH groups in zeolites with FAU and MFI structures. In addition, when modeling zeolite-supported metal clusters, the new approach implies considerably reduced corrections due to the basis set superposition error, compared to our previous scheme for treating the border region of the QM partition [J. Phys. Chem. B 2003, 107, 2228].