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Thermal expansion in dispersion-bound molecular crystals

Author(s): Ko, Hsin-Yu; DiStasio, Robert A; Santra, Biswajit; Car, Roberto

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Abstract: We explore how anharmonicity, nuclear quantum effects (NQE), many-body dispersion interactions, and Pauli repulsion influence thermal properties of dispersion-bound molecular crystals. Accounting for anharmonicity with ab initio molecular dynamics yields cell parameters accurate to within 2% of experiment for a set of pyridinelike molecular crystals at finite temperatures and pressures. From the experimental thermal expansion curve, we find that pyridine-I has a Debye temperature just above its melting point, indicating sizable NQE across the entire crystalline range of stability. We find that NQE lead to a substantial volume increase in pyridine-I (≈40% more than classical thermal expansion at 153 K) and attribute this to intermolecular Pauli repulsion promoted by intramolecular quantum fluctuations. When predicting delicate properties such as the thermal expansivity, we show that many-body dispersion interactions and more sophisticated density functional approximations improve the accuracy of the theoretical model.
Publication Date: 18-May-2018
Electronic Publication Date: 18-May-2018
Citation: Ko, Hsin-Yu, DiStasio, Robert A, Santra, Biswajit, Car, Roberto. (Thermal expansion in dispersion-bound molecular crystals. Physical Review Materials, 2 (5), 10.1103/physrevmaterials.2.055603
DOI: doi:10.1103/physrevmaterials.2.055603
EISSN: 2475-9953
Language: en
Type of Material: Journal Article
Journal/Proceeding Title: Physical Review Materials
Version: Author's manuscript

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