Rare event simulations reveal subtle key steps in aqueous silicate condensation

Area of Science:

• Computational Chemistry
• Materials Science
• Chemical Dynamics

Background:

• Silicate condensation is crucial for forming complex silicon-based materials.
• Understanding the early stages of this process is vital for controlling material properties.
• The precise mechanisms of monomer association, dissociation, and water removal remain incompletely understood.

Purpose of the Study:

• To elucidate the dynamics, thermodynamics, and reaction mechanisms of early-stage silicate condensation.
• To investigate the formation of a five-coordinated silicate dimer from monomers.
• To analyze dissociation and water removal pathways in both gas and aqueous phases.

Main Methods:

• Employed replica exchange transition interface sampling (RETIS) simulations.
• Utilized Born-Oppenheimer molecular dynamics (BOMD) for high-accuracy calculations.
• Simulated gas-phase association/dissociation and aqueous-phase dissociation/water removal.

Main Results:

• Identified two potential mechanisms for aqueous-phase silicate dimer dissociation, often involving proton transfer.
• Demonstrated that proton transfer predominantly dictates the nature of the resulting anionic silicate monomer.
• Revealed two water removal mechanisms, with direct proton transfer being slightly favored over water-mediated transfer.

Conclusions:

• Proton transfer plays a critical and predominant role in the early stages of silicate condensation.
• The direct proton transfer mechanism is slightly more favorable for water removal during silicate condensation.
• Computational simulations provide detailed insights into the complex reaction pathways governing silicate formation.