Dresden 2011 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 12: Postersitzung I
MM 12.12: Poster
Monday, March 14, 2011, 17:30–19:00, P5
Ab initio calculation of variable saddle point energies for atom jumps in L12 ordered Ni3Al — •Martin Leitner1,2, Doris Vogtenhuber3, Raimund Podloucky1, Wolfgang Pfeiler2, and Wolfgang Püschl2 — 1University of Vienna, Faculty of Chemistry, Department of Physical Chemistry — 2University of Vienna, Faculty of Physics, Department Dynamics of Condensed Systems — 3University of Vienna, Faculty of Physics, Department of Computational Materials Science
Kinetic Monte-Carlo simulation (KMC) in alloys is as good as the jump frequencies provided. According to transition state theory they are determined by a Boltzmann factor with the energy barrier to be surmounted, which is the difference between a saddle point and the initial state. This energy barrier explicitly depends on the atomic neighborhood of both states, especially on the configuration of the saddle point state. As an example for our arguments we take L12-ordered Ni3Al. It represents a class of technologically interesting intermetallic compounds where the highly ordered state leads to favorable properties (high-temperature strength, corrosion resistance,...). As in all fcc-type structures, atoms which jump into a nearest neighbor vacancy have to pass a four-atom window of common nearest neighbors. We discuss the substantial influence of the occupancy of this window on jump probabilities. For a classification of jump types, energy profiles were calculated from ab initio by using the VASP code. These results were entered into example KMC-simulations, demonstrating the large impact of variable saddle point energies on overall and detailed kinetics.