Regensburg 2013 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 50: Computational Materials Modelling - Defects & Interfaces I

MM 50.1: Vortrag

Donnerstag, 14. März 2013, 10:15–10:30, H24

Reconciling theory and experiment: Ab initio simulations of point defects up to the melting temperature — •Albert Glensk, Blazej Grabowski, Tilmann Hickel, and Joerg Neugebauer — Max-Planck-Institut für Eisenforschung, Düsseldorf

Experimental measurements of defect concentrations, enthalpies and entropies can be only performed at high temperatures close to the melting point. In contrast, presently employed T=0K and quasiharmonic DFT calculations are restricted to low temperatures. To bridge this gap a common approach is the extrapolation of the experimental data to T=0K assuming that the temperature dependence of the vacancy formation energy follows an Arrhenius behavior, i.e., that the defect entropy is independent on the temperature.

Using a newly developed approach we have been able to compute fully ab initio the temperature dependence of the defect formation energy from T=0K up to the melting point including all relevant free energy contributions, particularly also anharmonic contributions. Our results show a strong temperature dependence of the defect entropy resulting in a hitherto not expected strong non-Arrhenius behavior. Using the explicit temperature dependence we show that the T=0K extrapolated values reported in the literature are of by a few tenths of an eV for the formation energies and by an order of magnitude in the entropy. It will be shown that the revised energetics have severe consequences when using vacancy energies e.g. as benchmark to design new DFT xc functionals.