Molecular Density Functional Theory for water with liquid-gas coexistence and correct pressure

Abstract

The solvation of hydrophobic solutes in water is special because liquid and gas are almost at coexistence. In the common hypernetted chain approximation to integral equations, or equivalently in the homogenous reference fluid of molecular density functional theory, coexistence is not taken into account. Hydration structures and energies of nanometer-scale hydrophobic solutes are thus incorrect. In this article, we propose a bridge functional that corrects this thermodynamic inconsistency by introducing a metastable gas phase for the homogeneous solvent. We show how this can be done by a third order expansion of the functional around the bulk liquid density that imposes the right pressure and the correct second order derivatives. Although this theory is not limited to water, we apply it to study hydrophobic solvation in water at room temperature and pressure and compare the results to all-atom simulations. With this correction, molecular density functional theory gives, at a modest computational cost, quantitative hydration free energies and structures of small molecular solutes like n-alkanes, and of hard sphere solutes whose radii range from angstroms to nanometers. The macroscopic liquid-gas surface tension predicted by the theory is comparable to experiments. This theory gives an alternative to the empirical hard sphere bridge correction used so far by several authors.

18 pages, 6 figures

References in corpus (5)

• Molecular Density Functional Theory of Water
• Fast Computation of Solvation Free Energies with Molecular Density Functional Theory: Thermodynamic-Ensemble Partial Molar Volume Corrections
• Scalar fundamental measure theory for hard spheres in three dimensions. Application to hydrophobic solvation
• Integral equations for simple fluids in a general reference functional approach
• A molecular density functional theory to study solvation in water

Cited by in corpus (4)

• Efficient molecular density functional theory using generalized spherical harmonics expansions
• Density depletion and enhanced fluctuations in water near hydrophobic solutes: identifying the underlying physics
• Assessing the correctness of pressure correction to solvation theories in the study of electron transfer reactions
• Solvation in atomic liquids: connection between Gaussian field theory and density functional theory