Quantum Signature of Anisotropic Singularities in Hydrogen Bond Breaking of Water Dimer

Abstract In a recent paper, via three different semi-empirical methods, we reported quantum singularities of molecular electronic energies as signature of chemical bond break-up process in Rivastigmine drug molecule with torsion angle variation around -CO- bond revealed broken chemical moieties of Rivastigmine under experimental X-ray structure identification. In this present work, applying first principle methods of Hartree-Fock, Density Functional as well as Moller-Plesset techniques. we have reconfirmed the previous general predictions of singularities in molecular electronic energy with torsion angle variation around weak H-bond of water dimer. Due to quantum nature of chemical bond breaking process leading to break-point conditions in otherwise connected molecular topology, the singularities in electronic energy is also suggestive of classical large force as needed in bond-breaking process onset. In this paper, we have presented the details of these interesting findings studied on water dimer. These results of quantum singularities can be useful to improve current force field and to understand reaction chemistry involving bond-breaking under geometrical constrains.