Surface Structure and Stability of Partially Hydroxylated Silica Surfaces

Area of Science:

• Materials Science
• Computational Chemistry
• Surface Science

Background:

• Surface energies of silicates are critical for understanding brittle fracture.
• Surface relaxation through annealing and hydroxylation significantly reduces these energies.
• Molecular-level simulations offer a powerful approach to study surface phenomena.

Purpose of the Study:

• To investigate the impact of force field reactivity on silica surface structure and energy.
• To evaluate the performance of ClayFF and ReaxFF force fields in simulating surface hydroxylation.
• To compare simulation results with experimental data for both fracture and equilibrium surface energies.

Main Methods:

• Classical molecular dynamics (MD) simulations were employed.
• Simulations were performed on silica surfaces using ClayFF and ReaxFF force fields.
• Surface relaxation was achieved through annealing and hydroxylation processes.

Main Results:

• Unhydroxylated fracture surface energies were calculated as 5.1 J/m² (ClayFF) and 2.0 J/m² (ReaxFF).
• ClayFF results aligned with experimental fracture energies (4.5 J/m²), while ReaxFF underestimated them.
• Posthydroxylation, ReaxFF yielded surface energies (0.2 J/m²) consistent with experimental equilibrium values (∼0.35 J/m²).

Conclusions:

• Neither force field perfectly replicated both experimental fracture and equilibrium surface energies.
• ClayFF is suitable for simulating silica fracture, whereas ReaxFF is better for equilibrium states.
• Accurate surface energy calculations necessitate careful consideration of the surface state and appropriate force field selection.