Potential field within zeolite

Theoretical Model As a simple model we may represent the potential field within the zeolite by a symmetric three dimensional sinusoidal function ... 

The final methods which will be discussed are those which consider the electrostatic potential or field within a zeolite cage or skeleton, and the effect that this may have upon possible catalytic sites and absorbed molecules. A number of these calculations have been carried out, and they can be divided into two categories those which use the monopole approximation and simply calculate the field or potential due to point charges placed at atom centres , or those which use a more rigorous approach and calculate the potential directly from the molecular wavefunction . ... 

The molecular field distribution within the channels must be investigated, taking into consideration the structure of the zeolite, and the calculation of the potential energy of interaction between the zeolite and particular molecules must be made. These investigations would be assisted greatly by spectroscopic studies which would make it possible to establish the nature of the zeolite surface, the presence and the nature of structural defects, and the state of the adsorbed molecules. 

For inorganic systems, it has been more common to specify pairwise interaction parameters individually (see, e.g.. Ref. 86). This is a consequence of the historical emphasis on the simulation of a limited number of compounds within a particular study. However one notable exception is provided by the ionic potential parameters derived by Vessal (see Table 12 in the later section Zeolites and Microporous Materials). In his approach, combining rules were a design constraint in the derivation of the parameter set as a whole. The resulting force field is effective for both the structural and energetic description of a wide range of materials and, in particular, the incorporation of nonframework cations in microporous materials, which can prove an exacting test of more locally derived and less transferable force fields. 

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