Study of the stabilization energies of halide-water clusters: An application of first-principles interaction potentials based on a polarizable and flexible model

Abstract

The aim of this work is to compute the stabilization energy E stab (n) of ͓X(H 2 O) n ͔ Ϫ (XϵF, Br, and I for nϭ1 -60) clusters from Monte Carlo simulations using first-principles ab initio potentials. Stabilization energy of ͓X(H 2 O) n ͔ Ϫ clusters is defined as the difference between the vertical photodeachment energy of the cluster and the electron affinity of the isolated halide. On one hand, a study about the relation between cluster structure and the E stab (n) value, as well as the dependence of the latter with temperature is performed, on the other hand, a test on the reliability of our recently developed first-principles halide ion-water interaction potentials is carried out. Two different approximations were applied: ͑1͒ the Koopmans' theorem and ͑2͒ calculation of the difference between the interaction energy of ͓X(H 2 O) n ͔ Ϫ and ͓X(H 2 O) n ͔ clusters using the same ab initio interaction potentials. The developed methodology allows for using the same interaction potentials in the case of the ionic and neutral clusters with the proviso that the charge of the halide anion was switched off in the latter. That is, no specific parametrization of the interaction potentials to fit the magnitude under study was done. The good agreement between our predicted E stab (n) and experimental data allows us to validate the first-principles interaction potentials developed elsewhere and used in this study, and supports the fact that this magnitude is mainly determined by electrostatic factors, which can be described by our interaction potentials. No relation between the value of E stab (n) and the structure of clusters has been found. The diversity of E stab (n) values found for different clusters with similar interaction energy indicates the need for statistical information to properly estimate the stabilization energy of the halide anions. The effect of temperature in the prediction of the E stab (n) is not significant as long as it was high enough to avoid cluster trapping into local equilibrium configurations which guarantees an appropriate sampling of the configurational space. Parallel tempering method was applied in particular cases to guarantee satisfactory sampling of clusters at low temperature.

A Discrete Chloride Monohydrate: A Solid-State Structural and Spectroscopic Characterization

“…Understanding the nature of hydrated ions, especially the ubiquitous chloride ion, is essential to a wide variety of important areas, for example, atmospheric processes (aerosol formation and electric current transport), − materials science, and biomolecular processes such as ion-channel membrane transport. − It is thus important to our understanding of many fundamental aspects of chemistry, physics, biology, and geology. Unfortunately, there are relatively few techniques available to study discrete chloride hydrate species, their behavior in bulk solution, and their interactions in other environments such as cell membranes, so computational studies have been critical to our understanding of these systems. − Experimentally, the “messenger” atom technique (by the monitoring of argon predissociative mass loss) has been used to measure infrared spectra of simple anion–water clusters, and this has greatly facilitated the refinement of computational studies and the deepening of our understanding of such species and their dynamic processes. , More traditional solid-state structural studies on discrete chloride–water species have been very limited; the vast majority of structural studies involve one- to three-dimensional hydrogen-bonded networks. , This almost certainly arises because water has two proton donor groups and chloride can accept several proton donor groups. Also, the associated cation usually has strong interactions with the chloride ion via electrostatic forces and often hydrogen bonding.…”

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

“…Over the past two decades, several computational studies focussed on determining the structures, relative energies, and vibrational spectra of aqueous ionic clusters. [18][19][20][21][22][23][24] The molecular modeling of the hydration of halide ions is particularly challenging since halide-water H-bonds can perturb, in a nontrivial way, both structure and dynamics of the surrounding water H-bond network. 15 Moreover, the strength of the halide-water interactions varies significantly as function of ion size, charge density, and polarizability.…”

Specific Ion Effects on Hydrogen-Bond Rearrangements in the Halide–Dihydrate Complexes

“…Ion–water clusters are ideal systems to validate the ability of molecular models to characterize the molecular mechanisms associated with hydrogen-bonding (H-bonding) rearrangements, since, due to their relatively small sizes, they are amenable to high-level molecular modeling ,− and, at the same time, can be studied experimentally using high-resolution vibrational spectroscopy. − In this context, halide dihydrates hold a special place since they are the smallest complexes in which two water molecules can be simultaneously H-bonded to each other and to the ion, thus allowing for directly probing the interplay between ion–water and water–water interactions.…”