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arXiv · 1803.00536

Thermal Expansion in Dispersion-Bound Molecular Crystals

Hsin-Yu Ko·Robert A. DiStasio Jr.·Biswajit Santra·Roberto Car
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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 pyridine-like 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 ($\approx 40$% 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 sophisticated treatments of Pauli repulsion are needed in dispersion-bound molecular crystals.

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Hsin-Yu Ko, Robert A. DiStasio Jr., Biswajit Santra, Roberto Car. 2018-03-01. Thermal Expansion in Dispersion-Bound Molecular Crystals. https://doi.org/10.1103/physrevmaterials.2.055603

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