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Some spin and spin‐free aspects of coulomb correlation in molecules
Author(s) -
Luzanov A. V.
Publication year - 2012
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.24101
Subject(s) - coulomb , spin (aerodynamics) , spins , density matrix , physics , quantum mechanics , condensed matter physics , quantum , thermodynamics , electron
A spin component analysis of the cumulant (irreducible) density matrices is provided. In particular, the spin‐up spin‐down cumulant density matrix, π 2 αβ , is considered as the most general definition of the Coulomb‐hole density matrix. The local atomic cumulants produced from π 2 αβ , turn out to be the most important components of the atomic charge and spin correlators. These spin‐up spin‐down components, vanishing in the restricted Hartree–Fock model, reflect directly an effect of the Coulomb correlation on the generalized Wiberg bond order indices and Penney–Dirac bond orders. A spin‐free algorithm for computing spin correlators and related local spins is proposed. The algorithm is implemented numerically at full configuration interaction (FCI) and simple coupled‐cluster (CC) levels. The presented analysis is exemplified by some FCI and CC doubles computations on small hydrides and typical carbenes and cumulenes. © 2012 Wiley Periodicals, Inc.