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Science 26 November 1999:
Vol. 286. no. 5445, pp. 1705 - 1707
DOI: 10.1126/science.286.5445.1705
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Reports

First-Principles Determination of Elastic Anisotropy and Wave Velocities of MgO at Lower Mantle Conditions

B. B. Karki, 1 R. M. Wentzcovitch, 1 S. de Gironcoli, 2 S. Baroni 2

The individual elastic constants of magnesium oxide (MgO) have been determined throughout Earth's lower mantle (LM) pressure-temperature regime with density functional perturbation theory. It is shown that temperature effects on seismic observables (density, velocities, and anisotropy) are monotonically suppressed with increasing pressure. Therefore, at realistic LM conditions, the isotropic wave velocities of MgO remain comparable to seismic velocities, as previously noticed in athermal high-pressure calculations. Also, the predicted strong pressure-induced anisotropy is preserved toward the bottom of the LM, so lattice-preferred orientations in MgO may contribute substantially to the observed seismic anisotropy in the D" layer.

1 Department of Chemical Engineering and Materials Science, Minnesota Supercomputing Institute, University of Minnesota, Minneapolis, MN 55455, USA.
2 Scuola Internazionale Superiore di Studi Avanzati (SISSA), I-34014 Trieste, Italy.

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