Static and lattice vibrational energy differences between polymorphs

By J. Nyman, G. Day. 2015

268 citations recorded by the source corpus.

A computational study of 1061 experimentally determined crystal structures of 508 polymorphic organic molecules has been performed with state-of-the-art lattice energy minimisation methods, using a hybrid method that combines density functional theory intramolecular energies with an anisotropic atom–atom intermolecular model. Rigid molecule lattice dynamical calculations have also been performed to estimate the vibrational contributions to lattice free energies. Distributions of the differences in lattice energy, free energy, zero point energy, entropy and heat capacity between polymorphs are presented. Polymorphic lattice energy differences are typically very small: over half of polymorph pairs are separated by less than 2 kJ mol−1 and lattice energy differences exceed 7.2 kJ mol−1 in only 5% of cases. Unsurprisingly, vibrational contributions to polymorph free energy differences at ambient conditions are dominated by entropy differences. The distribution of vibrational energy differences is narrower than lattice energy differences, rarely exceeding 2 kJ mol−1. However, these relatively small vibrational free energy contributions are large enough to cause a re-ranking of polymorph stability below, or at, room temperature in 9% of the polymorph pairs.

Subfields: Atomic and Molecular Physics, and Optics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/13fa56924bfd45de3cf0cc38f0e21814a30ad9af

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In Atomic and Molecular Physics, and Optics

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Citations in the corpus

First‐principles modeling of molecular crystals: structures and stabilities, temperature and pressure (2017, background): “Thermal effects are usually neglected in state-of-the-art first-principles calculations but can completely change the relative stability and ordering of low-energy polymorphs.(27,28) Furthermore, even if the thermodynamically most stable polymorph at a finite temperature is modeled correctly, it mig”
CrystalExplorer model energies and energy frameworks: extension to metal coordination compounds, organic salts, solvates and open-shell systems (2017, background): “In their extensive computational study of a large number of polymorph pairs, Nyman & Day (2015) concluded: ‘polymorphic lattice energy differences are typically very small: over half of polymorph pairs are separated by less than 2 kJ mol 1 and lattice energy differences exceed 7.2 kJ mol 1 in only…”
The thermodynamic scale of inorganic crystalline metastability (2016, background): “This weak lattice cohesion yields a correspondingly small energy scale of accessible metastability (38).”