Assessing Many-Body Effects of Water Self-Ions. I: OH^–(H₂O)_n Clusters

Abstract

The importance of many-body effects in the hydration of the hydroxide ion (OH) is investigated through a systematic analysis of the many-body expansion of the interaction energy carried out at the CCSD(T) level of theory, extrapolated to the complete basis set limit, for the low-lying isomers of OH(HO) clusters, with n = 1-5. This is accomplished by partitioning individual fragments extracted from the whole clusters into "groups" that are classified by both the number of OH and water molecules and the hydrogen bonding connectivity within each fragment. With the aid of the absolutely localized molecular orbital energy decomposition analysis (ALMO-EDA) method, this structure-based partitioning is found to largely correlate with the character of different many-body interactions, such as cooperative and anticooperative hydrogen bonding, within each fragment. This analysis emphasizes the importance of a many-body representation of inductive electrostatics and charge transfer in modeling OH hydration. Furthermore, the rapid convergence of the many-body expansion of the interaction energy also suggests a rigorous path for the development of analytical potential energy functions capable of describing individual OH-water many-body terms, with chemical accuracy. Finally, a comparison between the reference CCSD(T) many-body interaction terms with the corresponding values obtained with various exchange-correlation functionals demonstrates that range-separated, dispersion-corrected, hybrid functionals exhibit the highest accuracy, while GGA functionals, with or without dispersion corrections, are inadequate to describe OH-water interactions.

Anticooperativity of FH···Cl− hydrogen bonds in [FH)nCl]− clusters (n = 1…6)

“…Structures of other clusters (with n > 3) look as expected from simple electrostatic model of repulsing FH fragments: (FH) 4 ÁÁÁCl − -tetrahedron, (FH) 5 ÁÁÁCl − -trigonal bipyramid (with nonequivalent two axial and three slightly shorter equatorial FHÁÁÁCl − hydrogen bonds), (FH) 6 ÁÁÁCl − -octahedron. Overall, as Hirshfeld atomic charges show (see Table S2 in ESI), upon transition from FHÁÁÁCl − to (FH) 6 ÁÁÁCl − there is significant monotonous charge transfer from chlorine to FH moieties. In all cases, hydrogen bonds FHÁÁÁCl − are linear (with a couple degree deviation for n = 2 and 3).…”

“…Several parameters calculated at the bond critical point were previously proposed to be a markers for hydrogen bonds with strong covalent character: -G/V < 1, H < 0 and H/ρ < 0. [92,93] Each of these parameters shows monotonous decrease of partially covalent character of hydrogen bond (from FHÁÁÁCl − to (FH) 6 Cl − , see Figure 5). In all cases for the complex FHÁÁÁCl − it is clearly pronounced that hydrogen bond has a strong covalent character, while the [(FH) 2 Cl] − complex lies at the cutoff line.…”

“…Besides, mechanisms of formation of such clusters is important for atmospheric chemistry studies and for investigations of interstellar clouds . There are a number of works devoted to experimental and theoretical studies of solvation processes . Special attention is paid to clusters stabilized by hydrogen bonds, such as ion clusters formed by common solvents (water, ammonia, and others).…”

“…[4] There are a number of works devoted to experimental and theoretical studies of solvation processes. [5,6] Special attention is paid to clusters stabilized by hydrogen bonds, such as ion clusters formed by common solvents (water, [7][8][9][10] ammonia, [11] and others [12,13] ). Coordination of solvent molecules around solvated anions by hydrogen bonding changes the local structure of the medium and lies at the heart of Hofmeister series.…”

Re‐weighted random series path integral simulations of molecular clusters: Applications to lithium solvated by a mixed Stockmayer cluster

“…Clusters are gas phase nano‐sized aggregates of matter, they are vitally important for technological advances, and can serve as model systems to untangle and simplify the investigation of otherwise intractable problems at the fundamental level using a combination of theoretical and experimental methods. The contributions along these two lines are so numerous that it would be impossible to provide a meaningful comprehensive review of the literature within the confines of a research article. One fundamental issue that can be addressed theoretically and experimentally using clusters is the determination of the nuclear quantum effects on the dynamics and thermodynamics of microsolvation.…”