title: Toward a Unique Definition of the Local Spin.
abstract: In this work, we demonstrate that there is a continuum of different formulations for the decomposition of ⟨Ŝ(2)⟩ that fulfills all physical requirements imposed to date. We introduce a new criterion based upon the behavior of single-electron systems to fix the value of the parameter defining that continuum, and thus we put forward a new general formula applicable for both single-determinant and correlated wave functions. The numerical implementation has been carried out in the three-dimensional physical space for several atomic definitions. A series of representative closed-shell and open-shell systems have been used to illustrate the performance of this new decomposition scheme against other existing approaches. Unlike other decompositions of ⟨Ŝ(2)⟩, the new scheme provides very small local-spin values for genuine diamagnetic molecules treated with correlated wave functions, in conformity with the physical expectations.
authors.affiliation: Department of Chemistry and Institute of Computational Chemistry, University of Girona , 17071 Girona, Catalonia, Spain.
authors.forename: Eloy
authors.initials: E
authors.lastname: Ramos-Cordoba
authors.affiliation: Department of Chemistry and Institute of Computational Chemistry, University of Girona , 17071 Girona, Catalonia, Spain.
authors.forename: Eduard
authors.initials: E
authors.lastname: Matito
authors.affiliation: Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences , H-1525 Budapest, P.O. Box 17, Hungary.
authors.forename: István
authors.initials: I
authors.lastname: Mayer
authors.affiliation: Department of Chemistry and Institute of Computational Chemistry, University of Girona , 17071 Girona, Catalonia, Spain.
authors.forename: Pedro
authors.initials: P
authors.lastname: Salvador