Determination of local spins by means of a spin-free treatment

Abstract

This work describes a Mulliken-type partitioning of the expectation value of the spin-squared operator corresponding to an N-electron system. Our algorithms, which are based on a spin-free formulation, predict appropriate spins for the molecular fragments (at equilibrium geometries and at dissociation limits) and can be applied to any spin symmetry. Numerical determinations performed in selected closed- and open-shell systems at correlated level are reported. A comparison between these results and their counterpart ones arising from other alternative approaches is analyzed in detail. © 2011 American Chemical Society.