Analysis of crystal polymorphism by Pixel and quantum chemical calculations

4 Analysis of crystal polymorphism by Pixel and quantum chemical calculations 

The Pixel intermolecular interaction energy decomposition allows a better understanding of the forces that are at the root of the phenomenon of polymorphism. Moreover, the same quantum chemical calculation (MP2/6-31G ) that provides the electron density for the Pixel calculation also provides total electronic energies and so, in principle, a way of also estimating intramolecular energy differences between polymorphs. 

In the case of BIYSEH, the large intramolecular energy difference is due to a different conformation at the ring, but is presumably enhanced by the low accuracy of both determinations (R factor around 9%). This is even more evident for TMETTS, where one of the structure determinations has an R factor as high as 20%, and for DMURAC and CABTUV, where the structure with the higher R factor has a much less stabilizing intramolecular energy. Apparently, such an explanation does not apply to the case of BEBMAX, where both crystal structures have a low factor, the molecular 

In view of the previous analysis, the systematic study of energy differences between polymorphs must be taken with a pinch of salt nevertheless, some undisputable 

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