Halide Ion Micro-Hydration: Structure, Energetics, and Spectroscopy of Small Halide–Water Clusters

Abstract

<div> <div> <div> <p>Replica exchange molecular dynamics simulations and vibrational spectroscopy calculations are performed using halide-water many-body potential energy functions to provide a bottom-up analysis of the structures, energetics, and hydrogen-bonding arrangements in X−(H2O)n=3−6 clusters, with X = F, Cl, Br, and I. Independently of the cluster size, it is found that all four halides prefer surface-type structures in which they occupy one of the vertices in the underlying three-dimensional hydrogen-bond networks. For fluoride-water clusters, this is in contrast with previous reports suggesting that fluoride prefers interior-type arrangements, where the ion is fully hydrated. These differences can be ascribed to the variability in how various molecular models are capable to reproduce the subtle interplay between halide-water and water-water interactions. Our results thus emphasize the importance of a correct representation of individual many-body contributions to the molecular interactions for a quantitative description of halide ion hydration. </p> </div> </div> </div>

Assessing Many-Body Effects of Water Self-Ions. II: H3O+(H2O)n Clusters

“…Here, each E kB term corresponds to the k-body contribution to the interaction energy and each x i collectively represents the coordinates of all atoms within the i th molecule. Building on the accuracy of MB-pol, many-body PEFs describing the interactions of halide and alkalimetal ions with water have recently been developed 41,42 and used in computer simulations to investigate the energetics, structures and vibrational spectra of small ion-water clusters [43][44][45][46] as well as the hydration structure of Cs + ions in solution. 47 In order to develop a model for H 3 O + -water and OH − -water interactions following the MB-nrg methodology, it is necessary to gain a cohesive picture of many-body effects inherent to these systems.…”