Ab initio studies of high-pressure structural transformations in silica

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Three successive pressure-induced structural transformations of stishovite (rutile-structure (Formula presented)) to denser phases are predicted by the first-principles pseudopotential method within the local-density approximation. The transition from the rutile to the orthorhombic (Formula presented) phase occurs at 47 GPa, the transition from the (Formula presented) to the (Formula presented) structure at 98 GPa, and finally the (Formula presented) phase transforms to the pyrite phase at 226 GPa. It is clearly illustrated that the first transition is associated with an elastic instability which arises from the strong coupling between elastic constants and the softening rutile (Formula presented) mode. The fully optimized structures of the four polymorphs of silica are obtained as a function of pressure. In addition, all zone-center transverse optic modes of the rutile and (Formula presented) phases are determined as a function of pressure. The results are in excellent agreement with available experimental data. © 1997 The American Physical Society.

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Physical Review B - Condensed Matter and Materials Physics

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