Fragments, definition optimization

Cluster model scheme and periodical method were used in the molecular model calculations of active sites of zeolite catalysts results of both approaches are presented and discussed in this review. In cluster models of zeolite structures hydrogen boundary atoms (H ) were used to saturate dangling bonds of the Si and Al atoms. Definite restrictions were imposed on the optimization of positions of these boundary H atoms. In the optimization, the geometry of an appropriate fragment of zeolite lattice was taken from the experimental X-ray diffraction data [7]. Only Si-H and Al-H bond distances were optimized, while the positions of other atoms (except M), as well as directions of 0-H bonds, were kept frozen. The M ion was allowed to move freely in the structure. 

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