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| - Elastic Polarizable Environment Cluster Embedding Approach for Covalent Oxides andZeolites Based on a Density Functional Method
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| - We present a new quantum mechanics/molecular mechanics (QM/MM) embedding approach for systemswith directional polar covalent bonds. This “covalent elastic polarizable environment” (covEPE) scheme featuresa variational treatment of an energy expression that includes all degrees of freedom of both the QM region(the “cluster”) and the MM regions (the “environment”). The method completely and explicitly includes boththe electrostatic and mechanical interactions between a QM model cluster and its environment. Monovalentpseudoatoms that represent real atoms of the material saturate the dangling bonds of the cluster; thesepseudoatoms belong simultaneously to the QM and MM regions. For a correct description of a pure silicaenvironment, we constructed a new force field of the shell-model type based on potential derived chargesinstead of formal charges. We implemented the covEPE approach in the density functional program ParaGaussand applied it to pure-silica and Al-containing chabazite, employing a generalized gradient approximation.These applications showed that calculated structural parameters and OH frequencies of bridging hydroxylgroups reproduce experimental data with good accuracy compared to other contemporary computationalmethods.
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