### Abstract

We report the results of a first-principles LAPW calculation of the equation-of-state, dynamic stability, and infrared-active transverse optic vibrational mode frequencies of CaSiO_{3} perovskite. A Birch-Murnaghan fit to the computed energy-volume relation of the cubic phase yields values of V_{o} = 45.62 Å^{3}, K_{o} = 227 GPa, and K_{o}′ = 4.29 for the thermally-corrected equation-of-state parameters. These values are in excellent agreement with recent quasi-hydrostatic compression data to 10 GPa, but significantly differ from values derived from higher pressure non-hydrostatic compression data. We calculate the volume dependence of the infrared-active TO mode frequencies using a frozen-phonon approach. The lowest frequency ferroic mode is predicted to occur near 228 cm^{-1} at ambient pressure and displays classic soft-mode behavior in the tensile regime, in quantitative agreement with earlier molecular and lattice dynamical calculations, based on empirical potentials. These established a link between the low frequency ferroic mode and the thermally activated crystalline-amorphous transition in a model CaSiO_{3} perovskite system. Our present calculations also reveal that the static cubic perovskite structure is unstable with respect to small octahedral rotations, corresponding to Brillouin zone edge dynamical instabilities, at ambient pressure and throughout the pressure range of the lower mantle. We speculate that coupling of the low frequency ferroic mode with octahedral tilting modes and strain lower the activation energy for the crystalline-amorphous transition.

Original language | English (US) |
---|---|

Pages (from-to) | 2725-2728 |

Number of pages | 4 |

Journal | Geophysical Research Letters |

Volume | 23 |

Issue number | 20 |

State | Published - 1996 |

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### ASJC Scopus subject areas

- Earth and Planetary Sciences (miscellaneous)

### Cite this

_{3}perovskite.

*Geophysical Research Letters*,

*23*(20), 2725-2728.

**First-principles calculation of the equation-of-state, stability, and polar optic modes of CaSiO _{3} perovskite.** / Chizmeshya, Andrew; Wolf, George; McMillan, Paul F.

Research output: Contribution to journal › Article

_{3}perovskite',

*Geophysical Research Letters*, vol. 23, no. 20, pp. 2725-2728.

_{3}perovskite. Geophysical Research Letters. 1996;23(20):2725-2728.

}

TY - JOUR

T1 - First-principles calculation of the equation-of-state, stability, and polar optic modes of CaSiO3 perovskite

AU - Chizmeshya, Andrew

AU - Wolf, George

AU - McMillan, Paul F.

PY - 1996

Y1 - 1996

N2 - We report the results of a first-principles LAPW calculation of the equation-of-state, dynamic stability, and infrared-active transverse optic vibrational mode frequencies of CaSiO3 perovskite. A Birch-Murnaghan fit to the computed energy-volume relation of the cubic phase yields values of Vo = 45.62 Å3, Ko = 227 GPa, and Ko′ = 4.29 for the thermally-corrected equation-of-state parameters. These values are in excellent agreement with recent quasi-hydrostatic compression data to 10 GPa, but significantly differ from values derived from higher pressure non-hydrostatic compression data. We calculate the volume dependence of the infrared-active TO mode frequencies using a frozen-phonon approach. The lowest frequency ferroic mode is predicted to occur near 228 cm-1 at ambient pressure and displays classic soft-mode behavior in the tensile regime, in quantitative agreement with earlier molecular and lattice dynamical calculations, based on empirical potentials. These established a link between the low frequency ferroic mode and the thermally activated crystalline-amorphous transition in a model CaSiO3 perovskite system. Our present calculations also reveal that the static cubic perovskite structure is unstable with respect to small octahedral rotations, corresponding to Brillouin zone edge dynamical instabilities, at ambient pressure and throughout the pressure range of the lower mantle. We speculate that coupling of the low frequency ferroic mode with octahedral tilting modes and strain lower the activation energy for the crystalline-amorphous transition.

AB - We report the results of a first-principles LAPW calculation of the equation-of-state, dynamic stability, and infrared-active transverse optic vibrational mode frequencies of CaSiO3 perovskite. A Birch-Murnaghan fit to the computed energy-volume relation of the cubic phase yields values of Vo = 45.62 Å3, Ko = 227 GPa, and Ko′ = 4.29 for the thermally-corrected equation-of-state parameters. These values are in excellent agreement with recent quasi-hydrostatic compression data to 10 GPa, but significantly differ from values derived from higher pressure non-hydrostatic compression data. We calculate the volume dependence of the infrared-active TO mode frequencies using a frozen-phonon approach. The lowest frequency ferroic mode is predicted to occur near 228 cm-1 at ambient pressure and displays classic soft-mode behavior in the tensile regime, in quantitative agreement with earlier molecular and lattice dynamical calculations, based on empirical potentials. These established a link between the low frequency ferroic mode and the thermally activated crystalline-amorphous transition in a model CaSiO3 perovskite system. Our present calculations also reveal that the static cubic perovskite structure is unstable with respect to small octahedral rotations, corresponding to Brillouin zone edge dynamical instabilities, at ambient pressure and throughout the pressure range of the lower mantle. We speculate that coupling of the low frequency ferroic mode with octahedral tilting modes and strain lower the activation energy for the crystalline-amorphous transition.

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M3 - Article

AN - SCOPUS:0030265188

VL - 23

SP - 2725

EP - 2728

JO - Geophysical Research Letters

JF - Geophysical Research Letters

SN - 0094-8276

IS - 20

ER -