## Abstract

Ab initio molecular dynamic (AIMD) simulations were performed to calculate the equation of state (EOS) of CaSiO_{3} perovskite at mantle pressure-temperature conditions. At temperatures above 2000 K, even though the hydrostatic crystal structure is metrically tetragonal in the pressure range of 13-123 GPa, the symmetry of the elastic moduli is consistent with cubic symmetry. Our results show that elastic constants and velocities are independent of temperature at constant volume. Referenced to room pressure and 2000 K, we find: Gru{combining double acute accent}neisen parameter is γ(V) = γ_{0}(V/V_{0})^{q} with γ_{0} = 1.53 and q = 1.02(5), and the Anderson Gru{combining double acute accent}neisen parameter is given by ( α / α_{0} ) = ( V / V_{0} )^{δT} in which α_{0} = 2.89 × 10^{-5} K^{-1} and δ_{T} = 4.09(5). Using the third order Birch Murnaghan equation of state to fit our data, we have for ambient P and T, K_{0} = 236.6(8) GPa, K^{′}_{0} = 3.99 ( 3 ), and V_{0} = 729.0(6) Å^{3}. Calculated acoustic velocities show the following P-T dependence: (∂ln V_{P}/∂V) _{T or P} = -1.9 × 10^{-3}; (∂ln V_{S}/∂V)_{T or P} = -1.5 × 10^{-3}; (∂ln V_{Φ}/∂V)_{T or P} = -2.4 × 10^{-3}; (∂ln V_{S}/∂ln V_{P}) _{T or P} = 0.79; (∂ln V_{S}/∂ln V_{Φ})_{T or P} = 0.63, indicating that the variations in bulk modulus overpower the variations in shear modulus. The bulk modulus of CaSiO_{3} perovskite is up to 10% lower than MgSiO_{3} perovskite under lower mantle conditions. The difference diminishes with pressure and temperature. The shear modulus of CaSiO_{3} perovskite is almost 25% lower compared with MgSiO_{3} perovskite for shallow lower mantle pressures and temperatures and about 3% lower at the base of the lower mantle. The difference in density of these two perovskite is about 3-4% for all conditions. Both the density and bulk modulus differ from PREM by less than 2% throughout the lower mantle. The shear modulus is ∼10% lower at shallow depths grading to ∼5% by the core-mantle boundary. Thus, the seismic velocity of CaSiO_{3} perovskite will be lower (0-6%) than PREM.

Original language | English (US) |
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Pages (from-to) | 249-259 |

Number of pages | 11 |

Journal | Physics of the Earth and Planetary Interiors |

Volume | 155 |

Issue number | 3-4 |

DOIs | |

State | Published - May 16 2006 |

## Keywords

- CaSiO perovskite
- Elastic constants
- Equations of state
- Gru{combining double acute accent}neisen parameters
- Lower mantle
- Thermal expansion
- Thermoelastic properties