Understanding the surface potential of water

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Surface Science

Background:

• Quantifying surface potential at the liquid-vapor interface is crucial for understanding interfacial phenomena.
• Discrepancies exist between theoretical models (ab initio charge density, partial charge models) and experimental measurements of surface potential.
• Existing models often yield different electric potentials, particularly in regions outside molecular interactions.

Purpose of the Study:

• To resolve inconsistencies in quantifying the surface potential of liquid water at the liquid-vapor interface.
• To compare ab initio electronic charge density and effective atomic partial charge models.
• To validate theoretical surface potential calculations against experimental techniques.

Main Methods:

• Utilized explicit ab initio electronic charge density calculations.
• Employed effective atomic partial charge models for liquid water.
• Compared computed electrostatic surface potentials with high-energy electron diffraction and electron holography measurements.
• Contrasted theoretical results with electrochemical measurements.

Main Results:

• Ab initio electronic charge density calculations provide a more accurate representation of the electrostatic surface potential compared to partial charge models.
• Computed surface potentials from quantum mechanical charge distributions show good agreement with high-energy electron diffraction and electron holography data.
• Significant discrepancies were observed when comparing computed potentials with electrochemical measurements.
• Identified specific regions of space that should be excluded for accurate comparison between computed and electrochemical surface potentials.

Conclusions:

• The study successfully resolved inconsistencies in surface potential quantification for liquid water.
• High-energy electron holography serves as a valuable benchmark for validating ab initio computed surface potentials.
• A novel interpretation of ab initio surface potentials is proposed, emphasizing the need for careful comparison with experimental data, particularly in electrochemistry.
• Recommendations are provided for refining comparisons between theoretical and electrochemical measurements by excluding certain spatial regions.