The frequencies of the phonon spectrum at zero wave vector, the contribution of the various model potential terms to potential energy, the dielectric constants, and the mode oscillator strengths of quartz at 25, 580 and 600°C have been calculated from a polarizable ion model. The mode softening of the soft mode is attributable to the change of the contribution of potential energy terms to potential energy. The elastic constants, the contribution of potential terms to the elastic constants, and the change of internal coordinates due to the elastic stress have also been calculated. The anomalous elastic behavior near the transition point results both from the unusually negative contribution of the short–range internal rotation forces to the elastic constants at 580°C and from the rather large contribution of the strong short–range stretching forces at 600°C.

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