Rozsa Viktor, Galli Giulia
Pritzker School of Molecular Engineering, The University of Chicago, Chicago, Illinois 60637, USA.
J Chem Phys. 2021 Apr 14;154(14):144501. doi: 10.1063/5.0046193.
The interaction of ions and water at high pressure and temperature plays a critical role in Earth and planetary science yet remains poorly understood. Aqueous fluids affect geochemical properties ranging from water phase stability to mineral solubility and reactivity. Here, we report first-principles molecular dynamics simulations of mono-valent ions (Li, K, Cl) as well as NaCl in liquid water at temperatures and pressures relevant to the Earth's upper mantle (11 GPa, 1000 K) and concentrations in the dilute limit (0.44-0.88 m), in the regime of ocean salinity. We find that, at extreme conditions, the average structural and vibrational properties of water are weakly affected by the presence of ions, beyond the first solvation shell, similar to what was observed at ambient conditions. We also find that the ionic conductivity of the liquid increases in the presence of ions by less than an order of magnitude and that the dielectric constant is moderately reduced by at most ∼10% at these conditions. Our findings may aid in the parameterization of deep earth water models developed to describe water-rock reactions.
离子与水在高压和高温下的相互作用在地球和行星科学中起着关键作用，但目前仍知之甚少。水性流体影响着从水相稳定性到矿物溶解度和反应性等一系列地球化学性质。在此，我们报告了单价离子（锂、钾、氯）以及氯化钠在与地球上地幔相关的温度和压力（11吉帕斯卡，1000开尔文）下、处于海洋盐度范围内的稀溶液极限浓度（0.44 - 0.88摩尔/千克）的液态水中的第一性原理分子动力学模拟。我们发现，在极端条件下，除了第一溶剂化壳层外，离子的存在对水的平均结构和振动性质影响微弱，这与在环境条件下观察到的情况类似。我们还发现，在这些条件下，离子的存在使液体的离子电导率增加不到一个数量级，并且介电常数最多适度降低约10%。我们的研究结果可能有助于为描述水 - 岩反应而开发的深部地球水模型进行参数化。
