Reactive force fields for aqueous and interfacial magnesium carbonate formation.

Area of Science:

• Computational chemistry
• Materials science
• Geochemistry

Background:

• Developing accurate force fields for magnesium (Mg) is crucial for understanding mineral-water interactions.
• Existing models often struggle to capture the complex behavior of Mg ions and their interactions with water and mineral surfaces.

Purpose of the Study:

• To create robust ReaxFF parameter sets for Mg/C/O/H systems in both aqueous and interfacial environments.
• To investigate the behavior of magnesium-containing minerals and their interfaces with water, particularly focusing on ion interactions and surface adsorption.

Main Methods:

• Developed two ReaxFF force fields: an aqueous one for Mg ions and an interfacial one for minerals.
• Parameterized and validated force fields against various Mg-bearing crystals and Mg²⁺-water binding energies.
• Applied the force fields to simulate forsterite-water and brucite-water interfaces, including bicarbonate interactions.

Main Results:

• Observed long-range proton transfer deprotonating bicarbonate to carbonate at mineral-water interfaces.
• Calculated an energy barrier (0.22 eV) for carbonate attachment to Mg surfaces, consistent with aqueous ion pairing.
• Found anisotropic and heterogeneous diffusion of hydroxide ions on mineral surfaces.

Conclusions:

• The new ReaxFF force fields accurately model Mg interactions in diverse chemical environments.
• The findings provide mechanistic insights into the experimentally observed rapid magnesite nucleation and growth under specific conditions.