Polarization effects in the simulation of lead (II) fluoride
Michael J Castiglione; Mark Wilson; Paul A Madden; Michael J Castiglione; Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QZ, UK; Mark Wilson; Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QZ, UK; Paul A Madden; Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QZ, UK
Журнал:
Journal of Physics: Condensed Matter
Дата:
1999-11-22
Аннотация:
An interionic potential to describe the interactions in PbF<sub>2</sub> is constructed from ab initio calculations. The potential is based upon formal ionic charges and includes polarization effects arising from the induced dipoles on both anions and cations. The cation polarization effects are shown to be crucial to explain observable differences between PbF<sub>2</sub> and alkaline-earth fluorides of comparable cation size (SrF<sub>2</sub> and BaF<sub>2</sub>). In particular, the lower transition pressure between the - (fluorite) and - (cotunnite) phases and the qualitative difference between the shapes of the phonon dispersion for PbF<sub>2</sub> and the alkaline earths are reproduced. Simulations show a transition to a superionic conducting state in the -phase, though at a temperature slightly higher than that observed experimentally. No ionic conduction is observed in the -phase at comparable temperatures, in agreement with experiment. The pattern of diffuse neutron scattering predicted by the simulations in the superionic domain is shown to reproduce the distinctive distribution of intensity observed experimentally.
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