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

Abstract

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.