Role of dispersion interactions in the polymorphism and entropic stabilization of the aspirin crystal

Aspirin has been used and studied for over a century but has only recently been shown to have an additional polymorphic form, known as form II. Since the two observed solid forms of aspirin are degenerate in terms of lattice energy, kinetic effects have been suggested to determine the metastability...

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Bibliographic Details
Published in:Physical review letters 2014-08, Vol.113 (5), p.055701-055701, Article 055701
Main Authors: Reilly, Anthony M, Tkatchenko, Alexandre
Format: Article
Language:English
Subjects:
Aspirin
Aspirin - chemistry
Crystallization
Crystals
Dispersions
Elastic Modulus
Elasticity
Electronics
Fluctuation
Free energy
Kinetics
Mathematical analysis
Models, Molecular
Stability
Thermodynamics
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Summary:Aspirin has been used and studied for over a century but has only recently been shown to have an additional polymorphic form, known as form II. Since the two observed solid forms of aspirin are degenerate in terms of lattice energy, kinetic effects have been suggested to determine the metastability of the less abundant form II. Here, first-principles calculations provide an alternative explanation based on free-energy differences at room temperature. The explicit consideration of many-body van der Waals interactions in the free energy demonstrates that the stability of the most abundant form of aspirin is due to a subtle coupling between collective electronic fluctuations and quantized lattice vibrations. In addition, a systematic analysis of the elastic properties of the two forms of aspirin rules out mechanical instability of form II as making it metastable.
ISSN:0031-9007
1079-7114
DOI:10.1103/physrevlett.113.055701