Despite much effort being devoted to the study of ionic aqueous solutions at the nanoscale, our fundamental understanding of the microscopic kinetic and thermodynamic behaviors in these systems remains largely incomplete. Herein, we reported the first 10 μs molecular dynamics simulation, providing evidence of the spontaneous formation of monolayer hexagonal honeycomb hydrated salts of XCl₂·6H₂O (X = Ba, Sr, Ca, and Mg) from electrolyte aqueous solutions confined in an angstrom-scale slit under ambient conditions. By using both the classical molecular dynamics simulations and the first-principles Born–Oppenheimer molecular dynamics simulations, we further demonstrated that the hydrated salts were stable not only at ambient temperature but also at elevated temperatures. This phenomenon of formation of hydrated salt in water is contrary to the conventional view. The free energy calculations and dehydration analyses indicated that the spontaneous formation of hydrated salts can be attributed to the interplay between ion hydration and Coulombic attractions in the highly confined water. In addition to providing molecular-level insights into the novel behavior of ionic aqueous solutions at the nanoscale, our findings may have implications for the future exploration of potential existence of water molecules in the saline deposits on hot planets.

中文翻译：

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纳米孔中单层水合盐形成的证据

尽管在纳米尺度上研究离子水溶液付出了很多努力，但我们对这些系统中微观动力学和热力学行为的基本理解在很大程度上仍然不完整。在此，我们报道了第一个 10 μs 分子动力学模拟，为 XCl ₂ ·6H _{2的单层六角蜂窝水合盐的自发形成提供了证据}O（X = Ba、Sr、Ca 和 Mg）来自环境条件下限制在埃级狭缝中的电解质水溶液。通过使用经典分子动力学模拟和第一性原理 Born-Oppenheimer 分子动力学模拟，我们进一步证明了水合盐不仅在环境温度下而且在高温下都是稳定的。这种在水中形成水合盐的现象与传统观点相反。自由能计算和脱水分析表明，水合盐的自发形成可归因于高度承压水中离子水合和库仑吸引力之间的相互作用。除了在分子水平上洞察纳米级离子水溶液的新行为外，