Regensburg 2007 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 17: Poster Session I (Nanostructures at Surfaces; Metal Substrates: Epitaxy and Growth; Methods: Scanning Probe Techniques; Phase Transitions)

O 17.72: Poster

Montag, 26. März 2007, 17:30–20:30, Poster C

Combined ab initio quantum-mechanical/molecular-mechanical molecular-dynamic simulations for Si(001) — Jan van Heys and •Eckhard Pehlke — Institut für Theoretische Physik und Astrophysik, Christian-Albrechts-Universität Kiel, 24098 Kiel

There is an ongoing interest in how fast and due to which mechanism surface atomic vibrations decay after an initial excitation by a fs laser-pulse. When such vibrational processes are to be simulated directly by ab initio molecular dynamics, slabs with a thickness of more than 1000 layers become inevitable in order to exclude artefacts due to unwanted back-reflections of phonons from the bottom surface of the slab. In order to carry through such simulations we have implemented a combined quantum-mechanical (for the surface atoms) and molecular-mechanical (for the atomic vibrations sufficiently far away from the surface) molecular-dynamics scheme. One should be extremely cautious, however, when choosing standard empirical potentials for the molecular-dynamics part of the simulation, because slight deficiencies of the empirical potentials to correctly describe the bulk-phonon dispersion may considerably flaw the calculated surface vibrational lifetimes. To circumvent this problem, we suggest to use a simulation with truly ab initio quality by using ab initio force constants up to 8th-nearest neighbors for the molecular-mechanical part of the simulations. Results for Si(001) using slabs with 6400 atoms and simulation times up to 10 ps will be presented.