Molecular modeling site characterization

The application of molecular modelling methods(MMM) to catalysis research have led to great advances in the fundamental understanding[l]. The recent developments in the computer hardware partly forms the cause of the success, whereas the user-friendly software availability is a major cause. Specific emphasis in this paper will be on the application of these techniques to zeolite research. Unlike several other heterogeneous catalysis, zeolites are highly crystalline and well characterized materials. The surfaces amenable for molecular approach and the catalytic active sites in zeolites are reported without any ambiguity. 

Give a comprehensice account on the Characterization of Site in Molecular Modeling. Give suitable examples to support your answer. 

Although numerous experiments and spectroscopic characterizations have been conducted on the Phillips catalyst, the precise structure of the active site on the silica surface, reduction of the surface chromate species during the induction period, the formation of the first chromium-carbon bond, and the mechanism for ethylene polymerization still need to be further clarified [11]. In order to achieve more specific information, molecular modeling approaches could provide a useful complement to the experiments and enable us to study these obscure mechanistic problems directly at the atomic and molecular level. In the last decade, very precise mechanistic pictures of the Cr-based polymerization catalysts have been obtained using different theoretical methods, especially through a combination of the experimental findings with theoretical calculations. 

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