Dresden 2006 – scientific programme

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DY: Dynamik und Statistische Physik

DY 46: Poster

DY 46.15: Poster

Thursday, March 30, 2006, 16:00–18:00, P1

The free energy calculations of a system with soft mode. — •Małgorzata Sternik and Krzysztof Parlinski — Institute of Nuclear Physics Polish Academy of Sciences, ul.Radzikowskiego 152, Kraków

In regular crystals, where all phonon modes are harmonic, the free energy is a sum of the ground-state energy and vibrational configurations of noninteracting harmonic phonons. Using this approach, we performed the first-principle free-energy calculations of the tetragonal and monoclinic phases of zirconia. [1] The free energy for a cubic ZrO₂ crystal, which possesses a soft mode, was calculated using the double-well energy-displacement relation. The soft mode branch was considered as an ensemble of independent anharmonic oscillators of the parabola-plus-gaussian, or of the 2-4 polynomial forms.

The anharmonic contributions were included to reproduce the cubic-to-tetragonal phase transition. [2] The first results show that the cubic phase cannot be stabilized within the framework of the independent oscillators approach. The negative result could be a consequence of two reasons, that the thermal expansion of crystals and the phonon-phonon interaction are neglected.

This work was partially supported by the Polish State Commitee of Scientific Research (KBN), grant no 1 P03B 104 26.

[1] J.Chem.Phys. 122, 064707 (2005)

[2] J.Chem.Phys. 123, in print