Löwdin's pairing theorem and some of its applications

Abstract

Löwdin's pairing theorem and its extension by Karadakov are briefly overviewed and some less usual applications (outside the original realm of the spin-projected theories) are discussed. These are pertinent to the theory of intermolecular interactions and to the construction of extremely localized, but non-orthogonal, molecular orbitals.

Keywords:

• Löwdin's pairing theorem
• pairing theorem
• Karadakov's extended pairing theorem
• intermolecular interactions
• complete basis limit
• extremely localized molecular orbitals

Acknowledgements

The author is grateful for the partial financial support of the Hungarian Scientific Research Fund (grant OTKA 71816). He also acknowledges Prof. Péter R. Surján for a valuable suggestion, and Dr. Andrea Hamza for reading the manuscript and useful comments.