Dresden 2014 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 26: Computational Materials Modelling IV - Phase transitions II

MM 26.3: Talk

Tuesday, April 1, 2014, 12:15–12:30, IFW D

Importance of anharmonic free energy contributions in an ab initio description of the hcp to bcc transition in Ti — •Dominique Korbmacher, Albert Glensk, Blazej Grabowski, Tilmann Hickel, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung, Düsseldorf, Germany

Ti and its alloys are a very important class of materials with various technical and medical applications. Further optimizing the properties of these alloys requires accurate and reliable phase diagrams. A recent and very promising approach is the construction of phase diagrams based on finite temperature ab initio simulations [1]. However, a critical and so far unresolved difficulty when dealing with Ti based systems is the dynamical instability of the Ti bcc phase at T=0 K.

In the present study, we investigate the hcp to bcc phase transition in Ti including the anharmonic contribution on a fully ab initio basis (density-functional theory). To overcome the long CPU simulation times typically involved in calculating anharmonicity, we use here the recently developed UP-TILD method [1]. We show that the low temperature hcp phase is well described when comparing with experimental data (e.g., heat capacity). For the high temperature bcc phase the dynamical stabilization due to phonon-phonon interaction is correctly predicted, but we show that the commonly used exchange-correlation functional (GGA-PBE) yields a too soft expansion and a too low phase transition temperature. We discuss whether alternative xc-functionals can improve the situation.

[1] B. Grabowski, et al., PRB 79, 134106 (2009).