Local Molecular Field Theory for Coulomb Interactions in Aqueous Solutions

Abstract

Coulomb interactions play a crucial role in a wide array of processes in aqueous solutions but present conceptual and computational challenges to both theory and simulations. We review recent developments in an approach addressing these challengeslocal molecular field (LMF) theory. LMF theory exploits an exact and physically suggestive separation of intermolecular Coulomb interactions into strong short-range and uniformly slowly varying long-range components. This allows us to accurately determine the averaged effects of the long-range components on the short-range structure using effective single particle fields and analytical corrections, greatly reducing the need for complex lattice summation techniques used in most standard approaches. The simplest use of these ideas in aqueous solutions leads to the short solvent (SS) model, where both solvent–solvent and solute–solvent Coulomb interactions have only short-range components. Here we use the SS model to give a simple description of pairing of nucleobases and biologically relevant ions in water.

Quantifying the Relevance of Long-Range Forces for Crystal Nucleation in Water

“…In previous work, the effectiveness of the SS model was demonstrated in modeling the pairing of monovalent ions, multivalent ions, and nucleobases. , Our motivation of the etiquette is that it should also be able to capture the correlations between urea molecules in the process of nucleation from aqueous solutions. By then, comparing the simulation results from the SS model to those from the GT model, we should be able to disentangle the roles of the short- and long-range interactions in such complex dynamical processes.…”

“…By exploiting the separation of Coulomb interactions into strong short-range and uniformly slowly varying long-range components, local molecular field (LMF) theory focuses on the very different roles the short- and long-range components of intermolecular interactions in determining relevant structural, − thermodynamic, − and dynamical properties − in nonuniform fluids. More specifically, based on the controlled approximations used in the LMF theory, the short solvent (SS) model , was developed to renormalize effective long-range interactions between intermolecular solute sites, while retaining only short-range interactions for other atomic site pairs. This approach significantly reduces the computational complexity of aqueous systems.…”

“…This approach significantly reduces the computational complexity of aqueous systems. The SS model has been applied to the association of ionic and hydrophobic solutes with great success. , However, the investigation of rare events in more complicated systems, such as nucleation of molecular systems in water, poses additional challenges in discerning solvent-mediated effects, particularly when assessing the collective system response to long-range interactions over large time scales.…”

Perfecting Liquid-State Theories with Machine Intelligence

“…4 The mean-field approximation can also be used to account for long-range interactions in molecular fluids and electrolyte solutions through a judicious selection of a reference system that reproduces the liquid structure. 5 While the distinct roles played by the intermolecular short-and long-range interactions in determining the properties of a dense fluid offer valuable insights, van der Waals-type theories encounter challenges when applied to associating fluids and liquid mixtures. 6 As a matter of fact, its performance deteriorates even for one-component simple liquids, as the thermodynamic condition departs from the triple point.…”

“…Given an analytical expression for the radial distribution functions of hard-sphere fluids and that for a pairwise additive potential describing intermolecular interactions, the van der Waals picture is capable of predicting the properties of simple liquids in the vicinity of the triple point . The mean-field approximation can also be used to account for long-range interactions in molecular fluids and electrolyte solutions through a judicious selection of a reference system that reproduces the liquid structure . While the distinct roles played by the intermolecular short- and long-range interactions in determining the properties of a dense fluid offer valuable insights, van der Waals-type theories encounter challenges when applied to associating fluids and liquid mixtures .…”