Extended molecular Ornstein-Zernike integral equation for fully anisotropic solute molecules: formulation in a...

Area of Science:

• Computational chemistry
• Statistical mechanics
• Physical chemistry

Background:

• Conventional molecular Ornstein-Zernike (MOZ) theory uses spherical harmonic expansion, limiting accuracy for complex solutes.
• Truncation of spherical harmonic expansion in MOZ leads to significant errors in numerical calculations.
• Accurate calculation of solvent distribution is crucial for understanding solvation thermodynamics.

Purpose of the Study:

• To formulate an extended molecular Ornstein-Zernike (XMOZ) integral equation applicable to solutes of arbitrary shape and solid surfaces.
• To overcome the limitations of spherical harmonic expansion truncation in conventional MOZ theory.
• To assess the accuracy and applicability of the XMOZ theory in calculating solvation thermodynamics.

Main Methods:

• Formulation of the XMOZ integral equation in a rectangular coordinate system, avoiding spherical harmonic expansion.
• Application of XMOZ theory using hypernetted-chain (HNC) and Kovalenko-Hirata approximations.
• Comparison of XMOZ results with conventional MOZ theory, molecular dynamics simulations, and 3D reference interaction site model (3D-RISM) theory.

Main Results:

• XMOZ theory successfully calculates spatial solvent distributions around complex solutes, such as a sphere-dumbbell complex.
• Calculated excess chemical potentials for water, methane, and alanine dipeptide using XMOZ/HNC show qualitatively reasonable results.
• The XMOZ theory demonstrates improved accuracy compared to conventional MOZ theory for complex molecular systems.

Conclusions:

• The XMOZ integral equation provides a robust and accurate method for calculating solvent distribution around arbitrary solutes and surfaces.
• XMOZ theory offers a valuable tool for solution chemistry, particularly for determining solvation thermodynamics.
• This extended formalism overcomes limitations of previous methods, enabling broader applications in computational chemistry.