Long-range interactions and the sign of natural amplitudes in two-electron systems.

  title={Long-range interactions and the sign of natural amplitudes in two-electron systems.},
  author={Klaas J. H. Giesbertz and Robert van Leeuwen},
  journal={The Journal of chemical physics},
  volume={139 10},
In singlet two-electron systems, the natural occupation numbers of the one-particle reduced density matrix are given as squares of the natural amplitudes which are defined as the expansion coefficients of the two-electron wave function in a natural orbital basis. In this work, we relate the sign of the natural amplitudes to the nature of the two-body interaction. We show that long-range Coulomb-type interactions are responsible for the appearance of positive amplitudes and give both analytical… 

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