On the density matrix of effectively unpaired electrons

This Letter describes the relationships between the density of effectively unpaired electrons and other tools as the cumulant of the second-order redu ced density matrix and the statistical population analysis. A topological p opulation analysis, based on the atoms in molecules (AIM) theory, is incorp orated in to the framework of the density of effectively unpaired electrons . Numerical determinations are carried out within this analysis in several systems and the results are compared with those of a more traditional Mulli ken approach. (C) 2001 Elsevier Science B.V. All rights reserved.