Molecular structural order and anomalies in liquid silica

Area of Science:

• Condensed matter physics
• Materials science
• Computational chemistry

Background:

• Understanding the behavior of liquid silica is crucial for materials science and geochemistry.
• Liquid water exhibits anomalous properties related to structural order and diffusion, prompting comparisons with other liquids.
• Molecular dynamics simulations are a powerful tool for investigating complex liquid systems.

Purpose of the Study:

• To investigate the relationship between structural order, diffusivity anomalies, and density anomalies in liquid silica.
• To quantify local structural order using orientational and translational order parameters.
• To compare the behavior of liquid silica with that of liquid water.

Main Methods:

• Molecular dynamics simulations were performed across various state points.
• Previously defined orientational and translational order parameters were used to quantify local structural order.
• Structural order, diffusivity, and thermodynamic properties were measured.

Main Results:

• Liquid silica shows a bimodal distribution of orientational order at intermediate densities.
• Compressing silica at a fixed temperature leads to a maximum in orientational order followed by a minimum in translational order.
• Unlike water, silica's translational order parameter minimum is broad, and its structurally anomalous regime does not overlap with diffusivity anomalies.

Conclusions:

• Liquid silica exhibits distinct anomalous behaviors compared to water, particularly in the coupling of structural order parameters and their relation to diffusivity anomalies.
• The study provides quantitative insights into the complex interplay of structure, dynamics, and thermodynamics in liquid silica.
• Findings contribute to a deeper understanding of glass-forming liquids and their unique properties.