Berlin 2015 – scientific programme

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O: Fachverband Oberflächenphysik

O 19: Frontiers of Electronic Structure Theory: Many-Body Effects on the Nano-Scale I

O 19.3: Talk

Tuesday, March 17, 2015, 11:15–11:30, MA 004

Phonons in Molecular Crystals: The Role of Collective van der Waals Interactions — •Johannes Hoja and Alexandre Tkatchenko — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany

By now, it is well established that dispersive van der Waals (vdW) interactions are crucial for the structure and stability of molecular crystals [1]. However, complete understanding of functionality of molecular crystals also requires a predictive description of response to external perturbations. Here we study the role of vdW interactions on phonons in molecular crystals. This subject is important since such low-frequency vibrations can be used to identify for instance drugs, explosives, and different polymorphic forms of molecular crystals. We studied the vibrational spectra of several molecular crystals with density-functional theory, including many-body dispersion interactions (DFT+MBD method). We find that long-range MBD effects can give rise to novel peaks in the phonon density of states [2], which can not be observed with a simple pairwise treatment of vdW interactions. We further discuss the nature of these vibrations and demonstrate a non-trivial connection between collective vdW interactions and entropy of molecular crystals.

[1] L. Kronik, A. Tkatchenko, Acc. Chem. Res. 47, 3208 (2014).

[2] A. M. Reilly, A. Tkatchenko, Phys. Rev. Lett. 113, 055701 (2014).