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Thermodynamic Properties From Static-Lattice Calculations with Soft Modes

Published online by Cambridge University Press:  01 February 2011

Graeme J. Ackland  and
Neil D. Drummond
Graeme J. Ackland
Affiliation:
Department of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 2LZ
Neil D. Drummond
Affiliation:
Department of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 2LZ
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Abstract

While phase transition pressures and zero temperature thermodynamic properties can be accurately determined from electronic structure calculation, transition temperatures are more problematic because of the need to sample phase space and quantise vibrations. The quasiharmonic method has proved extremely accurate for calculating thermodynamic properties up to 90% of the melting point without explicit phase space sampling for most materials, but has low temperature divergences for soft mode materials such as perovskites. Here we present a modified quasiharmonic method which avoids these difficulties. Using a simple model system, we demonstrate trends of behaviour in both the classical and quantum limits showing the importance of phonon quantisation in soft-mode behavior.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 718: Symposium D – Perovskite Materials , 2002 , D6.4
Copyright
Copyright © Materials Research Society 2002

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