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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.

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Abstract Molecular simulations from small molecules to large bio-macromolecules and polymer systems are routinely used to simulate thermodynamics properties of interests by molecular mechanics-based potentials. In a recent paper, via three different semi-empirical methods, we reported quantum singularities in molecular mechanics torsion potentials as signature of chemical bond break-up process revealed under experimental X-ray as broken chemical moieties. 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 the torsion potential for the case of water dimer that connects two water monomers by weak hydrogen bond. Due to quantum nature of chemical bond breaking process leading to break-point conditions in otherwise connected molecular topology aided by molecular mechanics based potentials, the singularities are also suggestive of large forces as onset in the bond-breaking process. We have presented the details of these novel interesting findings in this paper. These results of quantum singularities can have significant impacts to improve current force fields and can open up new areas we define as “Fracture Molecular Mechanics” or “Fracture Force Field” in overlap regions of molecular and quantum mechanics based approaches to explore and account for chemical bond-breaking mechanisms in molecular simulation techniques.