Analyzing effects of strong electron correlation within Kohn-Sham density-functional theory

Abstract

A density-functional-theory method for analyzing effects of strong electron correlation is presented, based on a single Kohn-Sham determinant. It yields the population of effectively unpaired (odd) electrons and depicts the strength of nondynamic correlation, both locally and globally. It provides also a quantitative estimate of localized magnetic moments without invoking symmetry-breaking procedures. Preliminary tests on some exemplary systems of strong correlation such as C${}_{2}$, Cr${}_{2}$, the NO dimer, and dissociating H${}_{2}$ and N${}_{2}$ are discussed in comparison with available post-Hartree-Fock wave-function studies. We show that the bond in C${}_{2}$ is unlikely to have diradical character in its ground state, but may have it in some excited state. The singlet ground state of the NO dimer, however, does have a diradical character of the bonding. Quite interestingly, the bond in Cr${}_{2}$ has a quad-radical nature.