Molecular dynamics (MD) simulations provide an accurate description of the mineral–fluid interface from the perspective of the atomistic level taking into account all atom interactions. This simulation approach is computationally expensive if applied to large molecular systems. Classical Fluid Density Functional Theory (f-DFT) delivers structural and thermodynamic information at comparatively small computational costs. Numerous applications of f-DFT for electrolytes neglect an explicit consideration of solvent. In this work, an unrestricted three-component model (3CM) of f-DFT was applied, which incorporates Lennard-Jones (LJ) attractions for the description of the short-range interactions of fluid–fluid and fluid–wall rather than the hard sphere repulsions, named DFT/LJ-3CM. The DFT/LJ-3CM model considers ions as charged LJ particles and treats solvent molecules as neutral LJ particles. To validate the performance of the DFT/LJ-3CM, the f-DFT calculations were compared with atomistic simulations for montmorillonite (Mnt) with various hydrated states in electrolyte solutions. This benchmarking was used to assess critically the advantages and limitations of the f-DFT model. The calibrated DFT/LJ-3CM model for Na and Ca Mnt was applied to calculate cation selectivity for the ion exchange equilibrium with effective ion radius and swelling behavior of Mnt. The predictions of the DFT/LJ-3CM model were found to be in good agreement with the atomistic simulations and experimental data under a wide range of conditions. At the same time, the DFT calculations were 3–4 orders of magnitude faster than conventional MD simulations. Thus, the DFT/LJ-3CM model can be a computationally effective alternative to atomistic simulation in providing structural and thermodynamic properties of fluid–clay mineral interfaces. The DFT/LJ-3CM model provides a robust approach, which can be used for upscaling in reactive transport simulators and modeling ion migration taking place under more complex thermo-chemo-hydro-mechanical conditions.

中文翻译：

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通过原子模拟和流体密度泛函理论对 Ca-Na 蒙脱石中的离子和溶剂性质进行比较建模

分子动力学 (MD) 模拟从原子水平的角度提供了矿物-流体界面的准确描述，同时考虑了所有原子相互作用。如果应用于大分子系统，这种模拟方法在计算上是昂贵的。经典流体密度泛函理论 (f-DFT) 以相对较小的计算成本提供结构和热力学信息。f-DFT 在电解质中的许多应用都忽略了对溶剂的明确考虑。在这项工作中，应用了 f-DFT 的无限制三分量模型 (3CM)，它结合了 Lennard-Jones (LJ) 吸引力，用于描述流体-流体和流体-壁的短程相互作用，而不是硬球体排斥，命名为 DFT/LJ-3CM。DFT/LJ-3CM 模型将离子视为带电 LJ 粒子，将溶剂分子视为中性 LJ 粒子。为了验证 DFT/LJ-3CM 的性能，将 f-DFT 计算与电解质溶液中具有各种水合状态的蒙脱石 (Mnt) 的原子模拟进行了比较。该基准测试用于批判性地评估 f-DFT 模型的优点和局限性。Na 和 Ca Mnt 的校准 DFT/LJ-3CM 模型用于计算离子交换平衡的阳离子选择性与有效离子半径和 Mnt 的溶胀行为。发现 DFT/LJ-3CM 模型的预测与各种条件下的原子模拟和实验数据非常吻合。同时，DFT 计算比传统的 MD 模拟快 3-4 个数量级。因此，在提供流体-粘土矿物界面的结构和热力学特性方面，DFT/LJ-3CM 模型可以成为原子模拟的有效计算替代方案。DFT/LJ-3CM 模型提供了一种稳健的方法，可用于在反应传输模拟器中进行升级，并对在更复杂的热-化学-水-机械条件下发生的离子迁移进行建模。