What is it about?
We performed the largest computational study to date to understand the energy differences between polymorphs or organic molecules. Over 500 pairs of polymorphs with known crystal structures were studied using state of the art lattice energy minimisation and lattice dynamics calculations. This has provided distributions of lattice energy, entropy and free energy differences between polymorphs.
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Why is it important?
Polymorphism of organic molecular crystals is important because the physical properties of materials are very strongly influenced by the arrangement of molecules in the material. This study is important because it informs us about the range of possible energy differences between polymorphs, and the relative importance of lattice eneregy and entropy differences, which influences the temperature dependence of polymorph relatve stabilities.
Perspectives
I have been frustrated for a long time by having limited empirical data relating the the maximum observable lattice energy differences between crystalline polymorphs. Computational methods for calculatiung lattice energies are getting accurate enough to give reliable relative energies, so we have decided to add to existing knowledge on polymorphism through a large scale computational study. We need to know these ranges of possible lattice energy differences, to inform computational methods for crystal structure prediction, as well as to interpret the potential importance of individual itermolecular interactions in determining a molecule's crystal structure.
Professor Graeme Day
University of Southampton
Read the Original
This page is a summary of: Static and lattice vibrational energy differences between polymorphs, CrystEngComm, January 2015, Royal Society of Chemistry,
DOI: 10.1039/c5ce00045a.
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