Understanding chemical coupling in cyclic versus compact water clusters with the Ehrenfest Force

• Published in: Chemical physics letters 2021-10, Vol.781, p.138983, Article 138983
• Main Authors: Xing, Hui, Yang, Yong, Nie, Xing, Xu, Tianlv, Kirk, Steven R., Jenkins, Samantha
• Format: Article
• Language: English
• Subjects: Cooperativity; Ehrenfest Force; Hydrogen bonding; QTAIM; Small water clusters
• ISSN: 0009-2614; 1873-4448
• DOI: 10.1016/j.cplett.2021.138983

The precession K′ of the Ehrenfest Force F(r) associated with the most preferred directions of electronic charge density accumulation for the H4--O1 BCP hydrogen-bond and O5-H4 BCP covalent-bond of (H2O)4 (left panel) that are strongly coupled and covalent-bond-like. The H2--O16 BCP hydrogen-bond and O1-H2 BCP covalent-bond of (H2O)6 (right panel) are strongly coupled and hydrogen-bond-like. The unmarked green spheres indicate the positions of the bond critical points (BCPs). The blue circles indicate hydrogen-bond BCPs and magenta circles indicate covalent-bond BCPs. [Display omitted] •Directional nature of the chemical coupling in the (H2O)6 and (H2O)4 clusters obtained.•Explained greater average strength of hydrogen-bonds in (H2O)4 compared with (H2O)6.•Visualized the nature of the two-way donation of sigma and hydrogen-bond character.•Calculated the precessions Kʹ for the Ehrenfest Force F(r) and compared with QTAIM Kʹ.•Explained why the Ehrenfest Force F(r) determines the chemical coupling in water. We explain why differences in the nature of the chemical coupling in the compact (H2O)6 cluster and cyclic (H2O)4 cluster results in relatively stronger hydrogen-bonds in (H2O)4 compared with (H2O)6. We have investigated and visualized the nature of the two-way donation of both covalent and hydrogen-bond character between covalent (sigma) and hydrogen-bonds. This was undertaken by calculating the precessions Kʹ of the eigenvectors around the bond-path for the Ehrenfest Force F(r) and compared with the corresponding QTAIM Kʹ. We explain the success of the Ehrenfest Force F(r) in determining the chemical coupling underlying the unusual strength of hydrogen-bonds in water.