Ionized water clusters , n = 2 to 6: A high‐accuracy study of structures and energetics

Abstract

Ionized water clusters, normalH2On+, have been of remarkable interest owing to their crucial roles in many chemical and biological processes. Small cationic water clusters normalH2On+, n = 2 to 6 serve as reasonable models for understanding the nature of the ionized water. In this study, employing high‐level ab initio quantum chemical methods, such as the density‐fitted orbital‐optimized linearized coupled‐cluster doubles (DF‐OLCCD), coupled‐cluster singles and doubles (CCSD), and coupled‐cluster singles and doubles with perturbative triples [CCSD(T)], a high‐accuracy study of structures and energetics for cationic water clusters [normalH2On+, n = 2‐6] is presented. In this study, 2 dimer, 8 trimer, 18 tetramer, 23 pentamer, and 25 hexamer clusters are reported. Most of the structures considered are reported for the first time. Relative, binding, and vertical attachment energies (VAEs), for the first time, are presented at the complete basis set (CBS) limit, extrapolating energies of the aug‐cc‐pVTZ and aug‐cc‐pVQZ basis sets, to provide the most accurate energetics to date. Our results demonstrate that as cluster size increases, the VAE value decreases, which indicates that large‐size clusters better compensate for the electron deficiency compared with small‐size clusters. The VAE values for pentamer and hexamer clusters are 118.5 to 165.5 and 121.9 to 153.7 kcal mol−1, respectively. Further, our binding energy results, at the CCSD(T)/CBS level, indicate strong bindings in cationic clusters due to hydrogen bond interactions. The average binding energy per water molecule varies from −16.6 to −21.8 kcal mol−1 for the clusters considered. Hence, we present the most extensive and accurate study on ionized water clusters to date. Further, our results indicate that the DF‐OLCCD method is very promising for ionic molecular clusters, and its accuracy approaches the CCSD(T) quality. The inexpensive analytic gradients of DF‐OLCCD, compared with CCSD(T), make it very helpful for high‐accuracy studies of molecular geometries.

Biologically Structured Water (BSW) - A Review (Part 3): Structured Water (SW) Generation, BSW Water, Bioenergetics, Consciousness and Coherence

“…These non-radical but reactive oxygen species react with the ions and hydroxyl radicals created during the water-splitting process at femtosecond intervals. Unal and Bozkava [15] conducted a computational study using quantum-based models to study hydroxylated water's structure, stability, and binding energy as it converted back into cationic water clusters (H 2 O) n + n=2-6. They also found that water clusters formed at the following frequency: 2 dimers, eight trimers, 18 tetramers, 23 pentamers, and 25 hexamer structures.…”

Mechanism of proton transport in water clusters and the effect of electric fields: A DFT study

“…However, the most stable water structure inside MOF-801 was found tetrahedral and cubic cavities are not in the liquid form but rather in the form of pentamer and octamer water cluster [19]. The structural properties of these cluster were reported earlier by using DFT calculations [20][21][22][23]. More recently, the hydrogen bonding structure of confined liquid water inside MOF was studied by Reith et al [24].…”

Infrared spectroscopy of [H2O–Xn]+(n= 1–3, X = N2, CO2, CO, and N2O) radical cation clusters: competition between hydrogen bond and hemibond formation of the water radical cation

“…, the (H 2 O) n + cluster, has been actively studied as the simplest model for ionization of water. 21–23,50–89 Some early theoretical calculations showed that the hemibond formation is preferred. However, many recent high-level theoretical computations agree well that the hemibonded form is less stable than the H-bonded form.…”