United atoms topological model

Definition and use of a united atom topological model (UATM) for the construction of the cavity [50]. The UATM reduces the number of spheres and then of tesserae. The frequency of divergence cases in the inversion of D is greatly reduced. The quality of the description of the solvent effects, measured by a difference between experimental and computed AG,oi values, is increased with respect to standard cavities. 

In all PCM methods, the radii of the spheres used to create the cavity can be further defined in different ways, but in the course of this thesis only the two most common radii have been employed the UAO and UFF. These two radii use the united atom topological model applied on atomic radii of the UFF force field for heavy atoms and only differ in how the spheres for hydrogen atoms are described. More specifically, in the UAO radii the hydrogen atoms are enclosed in the sphere of the heavy atom to which they are bonded, while in the UFF radii they have individual spheres. 

Figure 2. Representations of the three distinct topologies derived by simulated annealing based on data for a lithium gallosilicate (orthorhombic, Pna2i a = 18.5A, c = 7.5 A, 2 unique T-sites, 8 T-atoms in the unit cell) [66], The correct model (which proves isotopological with the parent zeolite Li-A(BW)) is (c).

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