Quasi-Chemical Theory for Anion Hydration and Specific Ion Effects: Cl${}^{-}$(aq) \emph{vs.} F${}^{-}$(aq)

Abstract

Anion hydration is complicated by H-bond donation between neighboring water molecules in addition to H-bond donation to the anion. This situation can lead to competing structures for chemically simple clusters like (H${}_2$O)${}_n$Cl${}^{-}$ and to anharmonic vibrational motions. Quasi-chemical theory builds from electronic structure treatment of isolated ion-water clusters, partitions the hydration free energy into inner-shell and outer-shell contributions, and provides a general statistical mechanical framework to study complications of anion hydration. The present study exploits dynamics calculations on isolated (H${}_2$O)${}_n$Cl${}^{-}$ clusters to account for anharmonicity, utilizing ADMP (atom-centered basis sets and density-matrix propagation) tools. Comparing singly hydrated F${}^{-}$ and Cl${}^{-}$ clusters, classic OH-bond donation to the anion occurs for F${}^{-}$, while Cl${}^{-}$ clusters exhibit more flexible but dipole-dominated interactions between ligand and ion. The predicted Cl${}^{-}$ -- F${}^{-}$ hydration free energy difference agrees well with experiment, a significant theoretical step for addressing issues like Hofmeister ranking and selectivity in ion channels.

arXiv comment17 pages, including Supporting Information, 10 figures

References in corpus (14)

• Separable Dual Space Gaussian Pseudo-potentials
• Perspective: How good is DFT for water?
• Tuning ion coordination preferences to enable selective permeation
• Ab initio molecular dynamics calculations of ion hydration free energies
• Real single ion solvation free energies with quantum mechanical simulation
• Quasi-Chemical and Structural Analysis of Polarizable Anion Hydration
• Quasi-chemical study of Be${}^{2+}$(aq) speciation
• Balancing Local Order and Long-Ranged Interactions in the Molecular Theory of Liquid Water
• On "the complete basis set limit" and plane-wave methods in first-principles simulations of water
• Self Consistent Molecular Field Theory for Packing in Classical Liquids
• Strontium and Barium in Aqueous Solution and a Potassium Channel Binding Site
• Regularizing binding energy distributions and thermodynamics of hydration. Application to water modeled with classical and ab initio simulations
• Quasi-Chemical Theory with Cluster Sampling from Ab Initio Molecular Dynamics: Fluoride (F${}^{-}$) Anion Hydration
• Concentration dependence of the Flory-Huggins interaction parameter in aqueous solutions of capped PEO chains

Cited by in corpus (1)

• Fast estimation of ion-pairing for screening electrolytes: A cluster can approximate a bulk liquid