Order Parameters and Algorithmic Approaches for Detection and Demarcation of Interfaces in Hydrate-Fluid and...

Area of Science:

• Computational physics and chemistry
• Materials science
• Chemical engineering

Background:

• Accurate characterization of solid-fluid interfaces is crucial in molecular dynamics simulations.
• Distinguishing between different solid phases, such as ice and hydrates, requires robust order parameters.
• Understanding interfacial properties like stiffness is essential for predicting material behavior.

Purpose of the Study:

• To examine the effectiveness of order parameter fields in molecular dynamics simulations for delimiting solid water phases (ice and hydrate).
• To investigate the influence of spatial sampling (meshes) and filtering on the quality of these order parameters.
• To assess the ability of selected order parameters to distinguish bulk phases, maintain consistency, resist noise, and define interface regions.

Main Methods:

• Utilized three order parameters: mass density (ρ), angular tetrahedrality measure (Sg), and water-dimer dihedral angle (F4).
• Analyzed spatial sampling and filtering techniques, including rectangular meshes and filtering.
• Employed autocorrelation maps to illustrate temporal features.
• Applied the capillary wave fluctuation method to estimate solid-fluid interfacial stiffnesses.

Main Results:

• Evaluated the performance of mass density, Sg, and F4 in distinguishing between bulk phases and defining interface regions.
• Assessed the consistency and noise susceptibility of the order parameters in various fluid environments (hydrophilic and hydrophobic).
• Partially succeeded in estimating solid-fluid interfacial stiffnesses for hydrophilic/hydrophobic interfaces using the capillary wave method.

Conclusions:

• Order parameter fields show potential for delimiting solid water phases in molecular dynamics simulations.
• Spatial sampling and filtering significantly impact the quality and reliability of these parameters.
• Further refinement is needed for accurate estimation of interfacial stiffnesses, particularly for complex interfaces.