Quantum Theory of Many-Particle Systems. I. Physical Interpretations by Means of Density Matrices, Natural Spin-Orbitals, and Convergence Problems in the Method of Configurational Interaction

@article{Lwdin1955QuantumTO,
  title={Quantum Theory of Many-Particle Systems. I. Physical Interpretations by Means of Density Matrices, Natural Spin-Orbitals, and Convergence Problems in the Method of Configurational Interaction},
  author={Per Olov L{\"o}wdin},
  journal={Physical Review},
  year={1955},
  volume={97},
  pages={1474-1489}
}
  • P. Löwdin
  • Published 15 March 1955
  • Mathematics
  • Physical Review
In order to calculate the average value of a physical quantity containing also many-particle interactions in a system of $N$ antisymmetric particles, a set of generalized density matrices are defined. In order to permit the investigation of the same physical situation in two complementary spaces, the Hermitean density matrix of order $k$ has two sets of indices of each $k$ variables, and it is further antisymmetric in each set of these indices. 

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