Accurate evaluation of the angular-dependent direct correlation function of water

Area of Science:

• Statistical Mechanics
• Liquid State Theory
• Computational Chemistry

Background:

• The direct correlation function (DCF) is crucial for understanding liquid thermodynamics.
• Accurate DCF calculation is essential for non-mean-field statistical theories.
• Previous methods lacked efficiency or accuracy for angular-dependent DCF.

Purpose of the Study:

• To develop an accurate and efficient procedure for calculating the angular-dependent DCF of bulk SPC/E water.
• To analyze the rotational invariant components of the DCF.
• To compute and discuss the angular-dependent bridge function of water.

Main Methods:

• Solving the molecular Ornstein-Zernike equation using simulation-derived total correlation functions.
• Polishing the DCF at small wavelengths for all orientations to match thermodynamic properties.
• Analyzing the DCF in terms of its rotational invariant components, specifically c112(r).

Main Results:

• An accurate and efficient method for computing the angular-dependent DCF of bulk SPC/E water was established.
• The dipolar symmetry component c112(r) was shown to reach its long-range behavior at 4 Å.
• The angular-dependent bridge function was computed and compared to hard-sphere bridge functions.

Conclusions:

• The developed DCF calculation method provides accurate thermodynamic and structural insights for water.
• Hard-sphere bridge functions, while useful for free energy calculations, are inadequate at a structural level for water.
• This work advances the understanding of liquid water structure and thermodynamics through advanced statistical mechanics.