Structure, Energetics, and Dynamics of Smectite Clay Interlayer Hydration: Molecular Dynamics and Metadynamics Investigation of Na-Hectorite

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• 作者：Christin P. Morrow ; A. 脰zg眉r Yazaydin ; Marimuthu Krishnan ; Geoffrey M. Bowers ; Andrey G. Kalinichev ; R. James Kirkpatrick
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：March 14, 2013
• 年：2013
• 卷：117
• 期：10
• 页码：5172-5187
• 全文大小：824K
• 年卷期：v.117,no.10(March 14, 2013)
• ISSN：1932-7455

文摘

This paper presents a classical molecular dynamics (MD) and metadynamics investigation of the relationships between the structure, energetics, and dynamics of Na-hydroxyhectorite and serves to provide additional, molecular-scale insight into the interlayer hydration of this mineral. The computational results support a model for interlayer H₂O structure and dynamics based on ²H NMR spectroscopy and indicate that H₂O molecules undergo simultaneous fast librational motions about the H₂O C₂ symmetry axis and site hopping with C₃ symmetry with respect to the surface normal. Hydration energy minima occur at one-, one-and-one-half-, and two-water-layer hydrates, which for the composition modeled correspond to 3, 5.5, and 10 H₂O/Na⁺, respectively. Na⁺ ions are coordinated by basal O atoms (O_MIN) at the lowest hydration levels and by H₂O molecules (O_H2O) in the two-layer hydrate, and H₂O molecules have an average of three H-bonds at the greatest hydration levels. The metadynamics calculations yield activation energies for site hopping of H₂O molecules of 6.0 kJ/mol for the one-layer structure and 3.3 kJ/mol for hopping between layers in the two-layer structure. Computed diffusion coefficients for water and Na⁺ are substantially less than in bulk liquid water, as expected in a nanoconfined environment, and are in good agreement with previous results.