Choosing the Right Structure

As mentioned earlier, many crystal structures can be generated for a given molecule, but judging the order of stability is a very difficult task. Use can be made here of the statistical relationships that have been outlined in the preceeding sections a list of possible tests follows  

1) check the final (PPE) of the optimized structure against the one expected from correlations to molecular parameters  

2) check the atomic contributions to (PPE) against the reference values provided in Table 12.4, and the distribution in shells, as in 12.3.2.3 (no strong repulsive contacts should be present)  

3) check the coordination sphere and the (PPE) distribution among symmetry operators (as in 12.4.3)  

4) the structure must be at equilibrium, that is, at the bottom of a potential energy well with respect to molecular displacements (see Section 12.3.3), and the lattice vibrational frequencies must be real. 

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Structure choice here are some hints to choose the right structure assignments if no structures are given to the sequences. 

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