title: Relationships between cumulant and spin-density matrices: application to the decomposition of spin.
abstract: This paper reports the derivation of a relationship between some elements of the cumulant matrix of the second-order reduced density matrix and the elements of the spin-density matrix. This relationship turns out to be very useful to determine local spins through the partitioning of the spin expectation value <S(2)> of an N-electron system. The procedure enables expression of both one- and two-center contributions only in terms of one-electron matrix elements, the elements of the spin-density matrix. We report numerical determinations of local spins in the Hilbert space of atomic orbitals in selected molecules and radicals in triplet and doublet states.
authors.affiliation: Departamento de Química Física, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apdo. 644 E48080 Bilbao, Spain.
authors.forename: Alicia
authors.initials: A
authors.lastname: Torre
authors.forename: Diego R
authors.initials: DR
authors.lastname: Alcoba
authors.forename: Luis
authors.initials: L
authors.lastname: Lain
authors.forename: Roberto C
authors.initials: RC
authors.lastname: Bochicchio