Cavity Particle in Aqueous Solution with a Hydrophobic Solute: Structure, Energetics, and Functionals

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Statistical Mechanics

Background:

• Calculating excess chemical potential is crucial for understanding solute behavior in solutions.
• Conventional DFT methods rely on direct correlation functions, which can be challenging to compute.
• Solvent-mediated interactions play a significant role in solvation phenomena.

Purpose of the Study:

• To formulate and apply endpoints density functional theory (DFT) for calculating the excess chemical potential of solutes.
• To connect endpoints DFT equations with conventional DFT expressions using indirect correlation functions.
• To investigate the solvent-mediated contribution (ω(x)) to the solute-solvent potential of mean force.

Main Methods:

• Formulated endpoints DFT equations in terms of the indirect contribution ω(x).
• Employed HNC and PY approximations to integrate the DFT charging integral.
• Performed molecular dynamics (MD) simulations at the pure solvent and solution endpoints.
• Analyzed a new approximation (two-points quadratic HNC) for the DFT charging integral.

Main Results:

• Calculated ω(x) and solute chemical potential for model systems with hydrophobic solutes of varying sizes in aqueous solution.
• Compared results from endpoints DFT with approximations when cavity particle data was unavailable.
• Demonstrated that the free energy of cavity particle insertion is not always negative for varying solute sizes.

Conclusions:

• The endpoints DFT method provides a viable framework for calculating excess chemical potential using readily accessible simulation data.
• The study highlights the importance of cavity particle behavior in solvation and the hydrophobic effect.
• The new two-points quadratic HNC approximation shows promise for improving DFT calculations.