Molecular theory of solvation: Methodology summary and illustrations

TL;DR

This paper reviews the integral equation theory of molecular liquids, especially the 3D-RISM method, highlighting its ability to efficiently predict solvation structures and thermodynamics in complex chemical and biomolecular systems.

Contribution

It summarizes the methodology of integral equation theory, focusing on the 3D-RISM approach with KH closure, and illustrates its advantages over molecular simulations for large-scale solvation problems.

Findings

3D-RISM accurately predicts solvation structures.

The method efficiently computes solvation free energies.

It handles large systems and slow processes beyond explicit simulations.

Abstract

Integral equation theory of molecular liquids based on statistical mechanics is quite promising as an essential part of multiscale methodology for chemical and biomolecular nanosystems in solution. Beginning with a molecular interaction potential force field, it uses diagrammatic analysis of the solvation free energy to derive integral equations for correlation functions between molecules in solution in the statistical-mechanical ensemble. The infinite chain of coupled integral equations for many-body correlation functions is reduced to a tractable form for 2- or 3-body correlations by applying the so-called closure relations. Solving these equations produces the solvation structure with accuracy comparable to molecular simulations that have converged but has a critical advantage of readily treating the effects and processes spanning over a large space and slow time scales, by far not feasible for explicit solvent molecular simulations. One of the versions of this formalism, the three-dimensional reference interaction site model (3D-RISM) integral equation complemented with the Kovalenko-Hirata (KH) closure approximation, yields the solvation structure in terms of 3D maps of correlation functions, including density distributions, of solvent interaction sites around a solute (supra)molecule with full consistent account for the effects of chemical functionalities of all species in the solution. The solvation free energy and the subsequent thermodynamics are then obtained at once as a simple integral of the 3D correlation functions by performing thermodynamic integration analytically.