Abstract:
Using the local-density approximation, calculating the Hellmann-Feynman forces, applying the direct method and deriving the phonon dispersion relations, the stability of the perovskite-like structures of MgSiO3 at T =0 have been studied. The cubic Pm\(Pm\overline 3 m\)m phase shows a dispersion-less soft phonon branch spreading from the R to M points of the cubic Brillouin zone. This soft branch persists up to high pressures of 150 GPa. The low-symmetry phases I4/mcm and Imma, P4/mbm can be considered as a result of the soft mode condensation at the M and R points, respectively. These phases prove to be unstable at T =0. The experimentally observed Pmnb phase is a consequence of the intersection of Imma and P4/mbm space groups. Thus, it can be regarded as a simultaneous condensation of two soft modes: one at the M and a second at the R high-symmetry points of the cubic Brillouin zone. The phonon dispersion relations of Pmnb show that this phase is stable and its optical phonons appear above 4.0 THz only.
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Received 15 October 1999 and Received in final form 14 January 2000
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Parlinski, K., Kawazoe, Y. Ab initio study of phonons and structural stabilities of the perovskite-type \(MgSi{O_3}\) . Eur. Phys. J. B 16, 49–58 (2000). https://doi.org/10.1007/s100510070248
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DOI: https://doi.org/10.1007/s100510070248