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arXiv physics/0505208physics.geo-ph
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地球深部地幔条件下液体MgSiO3的密度、粘度和扩散系数的第一性原理研究

First principles study of density, viscosity, and diffusion coefficients of liquid MgSiO3 at conditions of the Earth's deep mantle

Jones T. K. Wan, Thomas S. Duffy, Sandro Scandolo, Roberto Car

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6 pages, 3 figures
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摘要：

采用恒压恒温（\it ab initio）分子动力学模拟方法，对地球下地幔主要成分MgSiO $_3$液体进行了高温下的模拟研究。我们已经进行了可变细胞{ \it从头计算}分子动力学模拟在相关的热力学条件下测量的熔解曲线之一。计算的平衡体积和密度进行比较，在相同的条件下，使用正交钙钛矿配置的模拟。对于熔融MgSiO $_3$，我们测定了在不同热力学条件下的扩散系数和剪切粘度。我们的研究结果提供了新的限制熔融MgSiO $_3$的性质在核幔边界附近的条件。在所研究的压力-温度条件下，熔化体积变化为正，范围从88 GPa和3500 K时的5%到120 GPa和5000 K时的2.9%。然而，中性或负浮力熔体从（Mg，Fe）SiO $_3$钙钛矿组合物在深下地幔条件下是一致的固-液分配系数的Fe与现有的实验约束。我们的模拟结果表明，MgSiO $_3$是液体在120 GPa和4500 K，符合较低范围的实验熔化曲线，这种材料。线性外推的结果表明，液体和固体钙钛矿MgSiO $_3$的密度将变得相等接近180 GPa。

英文摘要：

Constant-pressure constant-temperature {\it ab initio} molecular dynamics simulations at high temperatures have been used to study MgSiO$_3$ liquid, the major constituent of the Earth's lower mantle to conditions of the Earth's core-mantle boundary (CMB). We have performed variable-cell {\it ab initio} molecular dynamic simulations at relevant thermodynamic conditions across one of the measured melting curves. The calculated equilibrium volumes and densities are compared with the simulations using an orthorhombic perovskite configuration under the same conditions. For molten MgSiO$_3$, we have determined the diffusion coefficients and shear viscosities at different thermodynamic conditions. Our results provide new constraints on the properties of molten MgSiO$_3$ at conditions near the core-mantle boundary. The volume change on fusion is positive throughout the pressure-temperature conditions examined and ranges from 5% at 88 GPa and 3500 K to 2.9% at 120 GPa and 5000 K. Nevertheless, neutral or negatively buoyant melts from (Mg,Fe)SiO$_3$ perovskite compositions at deep lower mantle conditions are consistent with existing experimental constraints on solid-liquid partition coefficients for Fe. Our simulations indicate that MgSiO$_3$ is liquid at 120 GPa and 4500 K, consistent with the lower range of experimental melting curves for this material. Linear extrapolation of our results indicates that the densities of liquid and solid perovskite MgSiO$_3$ will become equal near 180 GPa.

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