The recently determined phonon dispersion curves of alpha -quartz have been analysed with various polarizable-ion, bond-charge and shell models, the shell models giving a very satisfactory account of the dispersion curves as well as of the scattering intensities. Due to the use of interatomic potentials the number of free model parameters can be kept small. Investigating the dielectric constants in the framework of the developed shell models yields an ionic charge of about -2e for the oxygen ion, indicating a strongly ionic crystal. The polarizability of the O2- pseudo-ion in quartz should be close to 1.8 AA3. The physical significance of the obtained potentials has been tested by studying the equilibrium conditions. It turns out that additional valence forces of the Keating type improve the fulfilment of the equilibrium conditions, but that it is not possible to satisfy them completely.
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Schober et al. (1993) studied this question.
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