The determination of the speciation of ions and molecules in supercritical aqueous fluids under pressure is critical to understanding their mass transport in the Earth's interior. Unfortunately, there is no experimental technique yet available to directly characterize species dissolved in water at extreme conditions. Here we present a strategy, based on first-principles simulations, to determine ratios of Raman scattering cross-sections of aqueous species under extreme conditions, thus providing a key quantity that can be used, in conjunction with Raman measurements, to predict chemical speciation in aqueous fluids. Due to the importance of the Earth's carbon cycle, we focus on carbonate and bicarbonate ions. Our calculations up to 11 GPa and 1000 K indicate a higher concentration of bicarbonates in water than previously considered at conditions relevant to the Earth's upper mantle, with important implications for the transport of carbon in aqueous fluids in the Earth's interior.

中文翻译：

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确定超临界水中碳酸盐形态的第一原理方法。

确定压力下超临界水流体中离子和分子的形态对于了解它们在地球内部的质量传输至关重要。不幸的是，目前还没有实验技术可以直接表征极端条件下溶解在水中的物种。在这里，我们提出了一种基于第一性原理模拟的策略，以确定极端条件下水性物质的拉曼散射截面的比率，从而提供一个关键量，可与拉曼测量结合使用，以预测化学物种形成水性流体。由于地球碳循环的重要性，我们专注于碳酸盐和碳酸氢根离子。