Using first-principles density functional theory (DFT), we model the thermoelastic properties of hydrated ringwoodite (γ-(Fe, Mg)SiO), a potential water reservoir in the Earth's mantle transition zone (MTZ). Our calculations indicate that hydration, in general, leads to a reduction in the sound wave velocity of ringwoodite. However, increased pressure tends to suppress this reduction. For our 1.56 wt% HO containing ringwoodite model, we find that the suppression is so large that at pressure and temperature (P-T) conditions relevant to the lower part of the MTZ the sound wave velocities for the hydrous (1.56 wt% HO) ringwoodite become very similar to that of the anhydrous ringwoodite. However, when the water concentration is increased to 3.3 wt%, the pressure-induced suppression of the velocity reduction due to hydration is not so significant. We have given a plausible explanation for the same on the basis of the electronic structure of the hydrous ringwoodite models. We conclude that in the lower part of the MTZ, seismic wave data is sufficiently robust to detect regions of very high-water content (~3.3 wt%). However, if the water concentration is less than 1.56 wt%, sound wave velocities may not be able to precisely detect the state of hydration of the MTZ.

中文翻译：

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水对含铁尖角橄榄石热弹性性能的影响：第一性原理研究

利用第一性原理密度泛函理论 (DFT)，我们模拟了水合尖角橄榄石 (γ-(Fe, Mg)SiO) 的热弹性特性，水合尖角橄榄石是地幔过渡带 (MTZ) 中的潜在水库。我们的计算表明，水合作用通常会导致尖伍德石的声波速度降低。然而，增加的压力往往会抑制这种减少。对于我们的含 1.56 wt% H2O 的尖角橄榄石模型，我们发现抑制非常大，以至于在与 MTZ 下部相关的压力和温度 (PT) 条件下，含水 (1.56 wt% H2O) 尖角橄榄石的声波速度变为与无水尖晶石非常相似。然而，当水浓度增加到 3.3 wt% 时，压力引起的对水合速度降低的抑制就不那么明显了。我们基于水合尖晶石模型的电子结构对此给出了合理的解释。我们得出的结论是，在 MTZ 下部，地震波数据足够稳健，可以检测含水量非常高的区域 (~3.3 wt%)。然而，如果水浓度低于 1.56 wt%，声波速度可能无法精确检测 MTZ 的水合状态。