https://doi.org/10.1140/epjb/e2004-00166-1
Lattice dynamics and elastic properties of PbF2 and BaF2 from quantum mechanical calculations
1
Mineralogisches Institut, Johann Wolfgang Goethe-Universität,
Senckenberganlage 30, 60054 Frankfurt a.M., Germany
2
Institut für Geowissenschaften/Kristallographie, Christian Albrechts Universität,
Olshausenstr. 40, 24098 Kiel, Germany
3
Accelrys, 334 Cambridge Science Park,
Cambridge CB4 0WN, UK
Corresponding author: a b.winkler@kristall.uni-frankfurt.de
Received:
5
March
2004
Published online:
18
June
2004
The lattice dynamics of β-PbF2, α-PbF2 and cubic BaF2 were studied using density-functional perturbation theory. These calculations show that the bonding in the two PbF2 polymorphs is very similar. Phonon densities of states and heat capacities have been calculated and compared to the available experimental data. The results imply that anharmonicity begins to become significant already at temperatures as low as ~100 K. The computed elastic stiffness coefficients of the PbF2 polymorphs are used to discuss the unusual observation that the denser orthorhombic polymorph, thought to be the high pressure modification, is significantly more compressible than the cubic form.
PACS: 62.20.Dc – Elasticity, elastic constants / 63.20.Dj – Phonon states and bands, normal modes, and phonon dispersion / 65.40.Ba – Heat capacity / 71.15.Nc – Total energy and cohesive energy calculations
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2004
