Overlap repulsion with Löwdin's pairing theorem II. The leading term

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4 Citations (Scopus)


Recently, we derived an explicit analytical expression for the Heitler-London interaction energy between two "unperturbed" closed-shell molecules treated at the single determinant level, by using Löwdin's pairing theorem. Inspection of the results of the numerical calculations showed that for hydrogen-bonded systems the overlap of one pair of "corresponding orbitals" is always by one or more magnitudes larger than all the other ones. Keeping only the overlap of these "interacting orbitals" and neglecting all the others, one can obtain a great simplification in the expression of the intermolecular overlap effects without a significant loss in the accuracy. As expected, the interacting orbitals are localized in the region of the space where the distance between the two molecules is the shortest and can be considered as a bonding orbital between the proton donor and the hydrogen from one side and a lone pair of the proton acceptor from another.

Original languageEnglish
Pages (from-to)105-112
Number of pages8
JournalInternational Journal of Quantum Chemistry
Issue number3
Publication statusPublished - Mar 5 2001


  • Energy decomposition
  • Hydrogen bonding
  • Intermolecular interactions
  • Löwdin's pairing theorem
  • Overlap repulsion
  • Pairing theorem

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry

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