Berlin 2008 – wissenschaftliches Programm

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SYMS: Symposium Modern developments in multiphysics materials simulations

SYMS 3: Modern developments in multiphysics materials simulations III

SYMS 3.3: Vortrag

Freitag, 29. Februar 2008, 10:45–11:00, A 053

Conformational hierarchies of weakly bonded systems: Accuracy of dispersion corrected DFT — •Alexandre Tkatchenko, Volker Blum, and Matthias Scheffler — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin

It is well known that long-range dispersion interactions, important for stabilization of, e.g., molecular crystals, biomolecules and physisorption, are badly described by state-of-the-art xc functionals in DFT, but naturally included in post-HF or empirically in force field simulations. We have implemented a semi-empirical C₆/R⁶ correction [1,2] in the numeric atom-centered orbital based code FHI-aims [3] and obtained correction parameters by fitting to a database of high quality ab initio calculations [2], improving on previous results due to the more accurate basis set (0.5 kcal/mol average error for binding energies using PBE+C₆). We assess the accuracy and impact of the correction for a completely different class of systems; rather than testing the average properties of a database, we focus on conformational energy hierarchies of (i) (H₂O)_n clusters (n=2-6), (ii) Ala₂ and Ala₄, and (iii) infinite polyalanine conformers, comparing to published post-HF results for (i) and (ii). Even though the relative energies are not changed for small H₂O clusters and Ala₂ compared to DFT-GGA, the impact of dispersion on the conformation hierarchy of larger systems is surprisingly large, reaching ∼1-4 kcal/mol for different polyalanine conformers. [1] S. Grimme, J. Comput. Chem. 25, 1463 (2004) [2] P. Jurecka et al., J. Comput. Chem. 28, 555 (2007) [3] V. Blum et al., FHI ab initio molecular simulations (FHI-aims) project.