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MM: Fachverband Metall- und Materialphysik

MM 41: Materials design I

MM 41.2: Talk

Friday, March 30, 2007, 11:15–11:30, H16

Ab initio calculation of free energies and thermodynamic properties of fcc metals — •Blazej Grabowski, Tilmann Hickel, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Deutschland

Phase diagrams are indispensable tools in predicting material evolution during its processing. Current approaches to obtain such phase diagrams (e.g. CALPHAD) are based on an extra- and/or interpolation of experimental data. A crucial issue hampering this approach is the lack/high cost of specific experimental data (e.g. for unstable/metastable phases). For such cases, the replacement of experimental data by ab initio calculations is desirable.

The accuracy of density-functional based ab initio methods is, in principle, only limited by the exchange-correlation (XC) functional. We have therefore evaluated the accuracy of the most commonly used functionals (LDA, GGA) by calculating key thermodynamic properties for a large set of metals (Al, Pb, Cu, Ag, Au, Pd, Pt, Rh, Ir). Great care was taken to ensure that convergence errors due to supercell size, k-point sampling, and energy cutoff are small compared to the error in the XC-functional. Based on the volume and temperature dependence of free energies calculated in the quasiharmonic approximation, thermodynamic quantities such as the thermal expansion or the heat capacity have been derived. The comparison to experiment yields an excellent agreement. A detailed analysis shows that the LDA/GGA results can typically be considered as error bars allowing to estimate the accuracy of the calculation in the absence of experiments.