Ab initio structural and thermoelastic properties of orthorhombic MgSiO3 perovskite.

George Wolf, M. S T Bukowinski

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Abstract

Results are presented of an ab initio study of the structure and thermoelastic properties of orthorhombic (Pbnm) MgSiO3 perovskite as a function of T and P. Self-consistent free energies are computed using quasi-harmonic lattice dynamics, with interatomic potentials derived from an electron-gas formation. At high T the orthorhombic phase undergoes successive second-order transitions to tetragonal and cubic phases. The transition T increases with P, such that the orthorhombic phase is stable throughout most of the lower mantle, although higher symmetry phases could occur near the top of the lower mantle. At zero P the calculated bulk modulus and thermal expansion are in excellent agreement with available data. For high-T isotherms, a finite-strain decompression of the high-P equation of state of perovskite substantially overestimates its zero-P density and bulk modulus; hence constraints on the chemical composition of the lower mantle, based on a comparison of the decompressed seismological properties with zero-P laboratory data, may significantly overestimate the proportion of perovskite in the lower mantle. (Authors' abstract)-C.N.

Original languageEnglish (US)
Pages (from-to)809-812
Number of pages4
JournalGeophysical Research Letters
Volume12
Issue number12
StatePublished - 1985
Externally publishedYes

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perovskite
lower mantle
Earth mantle
bulk modulus
lattice dynamics
thermal expansion
pressure reduction
decompression
equation of state
electron gas
symmetry
proportion
chemical composition
isotherm
isotherms
equations of state
free energy
harmonics
electron
expansion

ASJC Scopus subject areas

  • Earth and Planetary Sciences (miscellaneous)

Cite this

Ab initio structural and thermoelastic properties of orthorhombic MgSiO3 perovskite. / Wolf, George; Bukowinski, M. S T.

In: Geophysical Research Letters, Vol. 12, No. 12, 1985, p. 809-812.

Research output: Contribution to journalArticle

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N2 - Results are presented of an ab initio study of the structure and thermoelastic properties of orthorhombic (Pbnm) MgSiO3 perovskite as a function of T and P. Self-consistent free energies are computed using quasi-harmonic lattice dynamics, with interatomic potentials derived from an electron-gas formation. At high T the orthorhombic phase undergoes successive second-order transitions to tetragonal and cubic phases. The transition T increases with P, such that the orthorhombic phase is stable throughout most of the lower mantle, although higher symmetry phases could occur near the top of the lower mantle. At zero P the calculated bulk modulus and thermal expansion are in excellent agreement with available data. For high-T isotherms, a finite-strain decompression of the high-P equation of state of perovskite substantially overestimates its zero-P density and bulk modulus; hence constraints on the chemical composition of the lower mantle, based on a comparison of the decompressed seismological properties with zero-P laboratory data, may significantly overestimate the proportion of perovskite in the lower mantle. (Authors' abstract)-C.N.

AB - Results are presented of an ab initio study of the structure and thermoelastic properties of orthorhombic (Pbnm) MgSiO3 perovskite as a function of T and P. Self-consistent free energies are computed using quasi-harmonic lattice dynamics, with interatomic potentials derived from an electron-gas formation. At high T the orthorhombic phase undergoes successive second-order transitions to tetragonal and cubic phases. The transition T increases with P, such that the orthorhombic phase is stable throughout most of the lower mantle, although higher symmetry phases could occur near the top of the lower mantle. At zero P the calculated bulk modulus and thermal expansion are in excellent agreement with available data. For high-T isotherms, a finite-strain decompression of the high-P equation of state of perovskite substantially overestimates its zero-P density and bulk modulus; hence constraints on the chemical composition of the lower mantle, based on a comparison of the decompressed seismological properties with zero-P laboratory data, may significantly overestimate the proportion of perovskite in the lower mantle. (Authors' abstract)-C.N.

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