A new method of evaluating the population of weakly paired electrons in strongly correlated systems is proposed for the first time within the framework of single-determinant Kohn-Sham density functional theory. The non-idempotency of the first order reduced density matrix that yields the odd-electron density is estimated within a real-space DFT model, rather than using multi-determinant wave functions. Some features of the relaxed exchange hole and the nondynamic correlation hole introduced in Becke's B05 model are employed here for this sake. The method is tested on a series of small molecules at different (stretched) bond lengths. The calculated dependence of the odd-electron population on the bond lengths shows a physically meaningful trend. The tests involve also some typical strongly correlated systems, such as Be2, C2, Cr2, and the NO dimer. The total mean number of odd electrons in such systems correlates well with the strength of nondynamic correlation from literature estimates. Particularly regarding the NO dimer, we show for the first time that the ground state singlet has a quad-radical character.

Free-radical population of strongly correlated electrons within Kohn-Sham density functional theory

244th National Meeting (2012)

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