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arXiv 2006.11501physics.chem-ph
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超临界水在大压温范围内的介电常数

Dielectric constant of supercritical water in a large pressure-temperature range

Rui Hou, Yuhui Quan, Ding Pan

摘要:

地球内部存在大量处于超临界状态的水,其介电性质在决定其如何储存和运输材料方面发挥着关键作用。然而,这是非常具有挑战性的,以获得静态介电常数的水,$ε_0$,在一个广泛的压力-温度(P-T)范围内发现在地球深部无论是实验还是第一性原理模拟。在这里,我们介绍了一个神经网络偶极子模型,结合分子动力学,可以用来计算的P-T依赖的水的介电性质的第一性原理方法一样准确,但更有效地。我们发现,$ε_0$在地球上地幔中可能会有一个数量级的变化,这表明水的溶剂化性质在不同深度会发生显着变化。分子的偶极矩和偶极角关联在控制$ε_0$的变化中有微妙的相互作用。我们还计算了水在微波范围内的频率依赖性介电常数,据我们所知,还没有从第一原理计算,并发现温度影响的介电吸收比压力。我们的结果在许多领域都有很大的用处,例如,在地球化学中模拟水-岩相互作用。这里介绍的计算方法可以很容易地应用到其他分子流体。

英文摘要:

A huge amount of water at supercritical conditions exists in Earth's interior, where its dielectric properties play a critical role in determining how it stores and transports materials. However, it is very challenging to obtain the static dielectric constant of water, $ε_0$, in a wide pressure-temperature (P-T) range as found in deep Earth either experimentally or by first-principles simulations. Here, we introduce a neural network dipole model, which, combined with molecular dynamics, can be used to compute P-T dependent dielectric properties of water as accurately as first-principles methods but much more efficiently. We found that $ε_0$ may vary by one order of magnitude in Earth's upper mantle, suggesting that the solvation properties of water change dramatically at different depths. There is a subtle interplay between the molecular dipole moment and the dipolar angular correlation in governing the change of $ε_0$. We also calculated the frequency-dependent dielectric constant of water in the microwave range, which, to the best of our knowledge, has not been calculated from first principles, and found that temperature affects the dielectric absorption more than pressure. Our results are of great use in many areas, e.g., modelling water-rock interactions in geochemistry. The computational approach introduced here can be readily applied to other molecular fluids.

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