title: Fractional spin in reduced density-matrix functional theory.
abstract: We study the behavior of different functionals of the one-body reduced density matrix (1RDM) for systems with fractional z-component of the total spin. We define these systems as ensembles of integer spin states. It is shown that, similarly to density functional theory, the error in the dissociation of diatomic molecules is directly related to the deviation from constancy of the atomic total energies as functions of the fractional spin. However, several functionals of the 1RDM show a size inconsistency which leads to additional errors. We also investigate the difference between a direct evaluation of the energy of an ensemble of integer-spin systems and a direct minimization of the energy of a fractional-spin system.
authors.affiliation: Nano-Bio Spectroscopy Group and ETSF Scientific Development Centre, Departamento Física de Materiales, Universidad del País Vasco, San Sebastián, Spain. nehelbig@gmail.com
authors.forename: N
authors.initials: N
authors.lastname: Helbig
authors.forename: G
authors.initials: G
authors.lastname: Theodorakopoulos
authors.forename: N N
authors.initials: NN
authors.lastname: Lathiotakis
mesh_terms: D000465:Algorithms; D008956:Models, Chemical; D011789:Quantum Theory