Abstract
This work describes the derivation of simple relationships between the density matrix of effectively unpaired electrons and the spin-density matrix in N-electron systems. The link between both devices turns out to be the one-electron matrix arising from the diagonal contraction of the cumulant matrix corresponding to the second-order reduced density matrix. We study some features of this contracted matrix, showing its usefulness to describe the electronic correlation. Numerical determinations performed in selected systems with different spin symmetries confirm the theoretical predictions.
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Acknowledgments
L.L. and A.T. acknowledge the Spanish Ministry of Science and Innovation for the grant No. CTQ2009-07459/BQU and the Universidad del País Vasco for the grant No. GIU09/43. D.R.A and R.C.B. acknowledge the support from the Projects X017 (Universidad de Buenos Aires) and PIP 11220090100061 (Consejo Nacional de Investigaciones Científicas y Técnicas). We thank the Universidad del País Vasco for allocation of computational resources.
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Published as part of the special issue celebrating theoretical and computational chemistry in Spain.
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Lain, L., Torre, A., Alcoba, D.R. et al. A study of the relationships between unpaired electron density, spin-density and cumulant matrices. Theor Chem Acc 128, 405–410 (2011). https://doi.org/10.1007/s00214-010-0795-6
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DOI: https://doi.org/10.1007/s00214-010-0795-6