# Berlin 2008 – wissenschaftliches Programm

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# MM: Fachverband Metall- und Materialphysik

## MM 51: Materials Design II

### MM 51.4: Vortrag

### Freitag, 29. Februar 2008, 12:30–12:45, H 0111

**Ab initio up to the melting point: Influence of vacancies and explicit anharmonicity** — •Blazej Grabowski, Lars Ismer, Tilmann Hickel, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung GmbH, Max-Planck Str. 1, 40237 Düsseldorf, Deutschland

A recent study [1] on an extensive set of elementary metals showed that a wide variety of thermodynamic properties can be excellently reproduced within the quasiharmonic approximation. An exception is the heat capacity which shows a clear deviation from experiment at temperatures above 70% of the melting temperature.

To clarify the origin of the nonlinear increase, we have investigated two potential candidate mechanisms being debated controversially in the literature. On the one hand, we have calculated the contribution of monovacancies to the free energy. We have included the vibrational entropy of the vacancy using the full volume dependent dynamical matrix (quasiharmonic approximation). On the other hand, we have calculated the contribution of the volume dependent explicit anharmonicity (of the pure crystal) to the free energy. For this purpose, we have employed thermodynamic integration. We find that both contributions are of equal magnitude and correct the quasiharmonic results when compared to experiment.

[1] Grabowski B., Hickel T., and Neugebauer J., PRB 76, 024309 (2007).