arXiv 2409.149322024-09-23astro-ph.EP

行星条件下硅水混合物中的线性混合近似

The linear-mixing approximation in silica-water mixtures at planetary conditions

Valiantsin Darafeyeu, Stephanie Rimle, Guglielmo Mazzola, Ravit Helled

备注：: Accepted for publication in ApJ
发表信息：: The Astrophysical Journal 975 (2), 255, 2024
DOI：: 10.3847/1538-4357/ad7e29

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AI总结：

本文评估了线性混合近似（LMA）在天王星和海王星内部压力-温度条件下计算硅水混合物状态方程的准确性，通过MD模拟发现其在150-600 GPa内误差小于5%，岩石会延迟超离子水转变，电子理论选择影响密度精度。

摘要：

线性混合近似（LMA）常用于行星模型中计算混合物的状态方程（EoSs）。行星组成中常见的假设是岩石与水的混合物。本文评估了LMA在天王星和海王星内部相关压力-温度条件下的准确性。我们使用从头算模拟进行分子动力学（MD）模拟，考虑了纯水、纯硅以及分子分数为1:1和1:4的硅水混合物，温度为3000 K，压力范围为30至600 GPa。我们发现，在约150-600 GPa范围内，LMA的误差在几个百分点内（<~5%），推断密度差异的符号取决于混合物的具体组成。我们还表明，对于1:4的硅水混合物，岩石的存在将向超离子水的转变延迟了约70 GPa。最后，我们注意到电子理论（泛函）的选择会影响状态方程，并在密度中引入约10%的不确定性。我们的研究证明了行星条件下相图的复杂性，以及更好地理解岩石-水混合物及其对推断行星组成影响的必要性。

英文摘要：

The Linear Mixing Approximation (LMA) is often used in planetary models for calculating the equations of state (EoSs) of mixtures. A commonly assumed planetary composition is a mixture of rock and water. Here we assess the accuracy of the LMA for pressure-temperature conditions relevant to the interiors of Uranus and Neptune. We perform MD simulations using ab-initio simulations and consider pure-water, pure-silica, and 1:1 and 1:4 silica-water molecular fractions at temperature of 3000 K and pressures between 30 and 600 GPa. We find that the LMA is valid within a few percent (<~5%) between ~150-600 Gpa, where the sign of the difference in inferred density depends on the specific composition of the mixture. We also show that the presence of rocks delays the transition to superionic water by ~70 GPa for the 1:4 silica-water mixture. Finally, we note that the choice of electronic theory (functionals) affect the EoS and introduces an uncertainty in of the order of 10% in density. Our study demonstrates the complexity of phase diagrams in planetary conditions and the need for a better understanding of rock-water mixtures and their effect on the inferred planetary composition.

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