Berlin 2018 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 82: Poster Focus Session: Frontiers of Electronic-Structure Theory - Correlated Electron Materials

O 82.7: Poster

Mittwoch, 14. März 2018, 18:15–20:30, Poster A

Ab-initio structural relaxation of molecular crystals under pressure — •Eric Pierschel, Pasquale Pavone, and Claudia Draxl — Humboldt-Universität zu Berlin, Physics Department and IRIS Adlershof, Germany

The structural relaxation of molecular crystals presents serious difficulties. In principle, forces acting on the atoms, calculated as energy gradients, allows for the search of the molecular configuration with the minimum possible energy. The drawback of this method is that the forces between atoms belonging to a single molecule are significantly stronger than the ones between atoms in different molecules. This makes the numerical determination of the orientation of molecules with respect to each other very difficult. To avoid this problem, we use a cluster algorithm which, first, detects individual molecules. Then, independent translations and rotations for each molecule are added to the list of the standard 3N degrees of freedom, corresponding to the N atoms in the unit cell. The structure optimization is performed in this overdetermined parameter space by using the BFGS-algorithm. Optionally, our procedure allows for performing the optimization of the molecular degrees of freedom only, by considering each molecule as a rigid rotator. We use this approach for relaxing molecular crystals, like the oligo-acens, under pressure. Ab-initio total energies are calculated using density-functional theory including van-der Waals interactions as implemented in the full-potential all-electron code T1lmttbnexciting.