### Abstract

Using Löwdin's pairing theorem one can obtain an explicit expression for the overlap repulsion of two "unperturbed" closed-shell molecules at the single determinant level. After some regrouping, the interaction energy can be presented as a sum of terms of different physical meaning, each of which is expressed explicitly in terms of the (paired) molecular orbitals of the interacting molecules. The interaction energy can be decomposed into the following terms: the "naive" electrostatic interaction corresponding to undisturbed charge distributions of the two molecules; the Hartree-Fock exchange calculated neglecting the orbital overlap; "finite basis" terms originating from the deviation of the individual molecular orbitals (MOs) from the Hartree-Fock limit; overlap effects modifying the intramolecular energies as well as the electrostatic and exchange interactions; "true" overlap effects containing intermolecular overlap integrals and intermolecular charge distributions in the one- or two-electron integrals.

Original language | English |
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Pages (from-to) | 53-59 |

Number of pages | 7 |

Journal | International Journal of Quantum Chemistry |

Volume | 82 |

Issue number | 2 |

DOIs | |

Publication status | Published - Mar 15 2001 |

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### Keywords

- Energy decomposition
- Energy decomposition for intermolecular interactions
- 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