Regensburg 2019 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 34: Methods in Computational Materials Modelling (methodological aspects, numerics)

MM 34.3: Talk

Thursday, April 4, 2019, 10:45–11:00, H44

Ab initio benchmark of anharmonic free energies in naphtalene — •Marcin Krynski, Nathaniel Raimbault, and Mariana Rossi — Fritz Haber Insitute of the Max Planck Society, Berlin, Germany

Organic molecular crystals are a vast group of compounds with undisputed industry importance, known for their ability to form polymorphs with properties tied strongly to their crystallographic structure. A large body of theoretical research is centered on polymorph energy ranking [1], which is impacted by the (often neglected) thermodynamic conditions and anharmonicities of the potential energy surface (PES). We present a study of anharmonic contributions to the free energies of the p21a14 and p21c14 molecular crystal polymorphs of naphthalene. We employ dispersion-corrected density-functional theory and compare full anharmonic free-energy evaluations [2] to more computationally tractable approximate methods, gauging the effect of lattice expansion at different temperatures. We show that at the PES, p21c14 is lower in energy than p21a14 by ca. 3meV/molecule for any combination of PBE/PBE0/B3LYP with pairwise or many-body van der Waals (vdW) corrections. Without vdW corrections, the crystals are not stable. We assess whether temperature and lattice expansion explain the experimentally observed stability of the p21a14 polymorph and extend our methodology to polymorphs of pimelic acid, which shows a puzzling temperature-dependent lattice contraction along one axis. [1] A. Reilly et al., Acta Cryst. B 72, 439 (2016); [2] M. Rossi, P. Gasparotto, M. Ceriotti, PRL 117, 115702 (2016)