Ion Distribution and Cation Exchange at Mica-Electrolyte Interfaces Probed with Deep Potential Molecular Dynamics

Area of Science:

• Geochemistry
• Computational Chemistry
• Materials Science

Background:

• Understanding ion behavior at mineral-aqueous interfaces is key for environmental and technological applications.
• Classical molecular dynamics (MD) simulations are limited by empirical force fields, necessitating advanced methods.

Purpose of the Study:

• To investigate the Stern layer structure and cation exchange mechanism at muscovite mica-electrolyte interfaces.
• To explore ion distribution and dynamics using advanced simulation techniques.

Main Methods:

• Nanosecond time scale MD simulations utilizing deep neural network interatomic potentials.
• Potentials were trained on density functional theory (DFT) data for accuracy.
• Simulations focused on K+ and Na+ at mica-electrolyte interfaces with varying salt solutions (NaCl, KCl).

Main Results:

• Potassium ions (K+) predominantly adopt inner-sphere configurations, while sodium ions (Na+) show significant outer-sphere populations.
• Coadsorption of multiple cation species leads to local surface overcharging.
• This overcharging reshapes cation speciation, promoting the desorption of neighboring surface cations.

Conclusions:

• The study provides a detailed molecular-level understanding of cation exchange at the muscovite-water interface.
• Findings align with experimental observations of altered cation speciation and slow kinetics due to coadsorption.
• This work offers a foundation for interpreting experimental data and predicting interfacial behavior.