title: Restricted Ensemble-Referenced Kohn-Sham versus Broken Symmetry Approaches in Density Functional Theory:  Magnetic Coupling in Cu Binuclear Complexes.
abstract: The performance of density functional theory in estimating the magnetic coupling constant in a series of Cu(II) binuclear complexes is investigated by making use of two open shell formalisms:  the broken symmetry and the spin-restricted ensemble-referenced Kohn-Sham methods. The strong dependence of the calculated magnetic coupling constants with respect to the exchange-correlation functional is confirmed and found to be independent of whether spin symmetry is imposed or not. The use of a method which guarantees the spin state does not improve the correlation with the experiment and indeed shows some worsening due to an overestimation of the ferromagnetic interactions. However, with the present exchange-correlation functionals, a rather systematic deviation is found. Therefore, it would be possible to develop improved density functionals which will allow for a rigorous treatment of open shell systems in density functional theory.
authors.affiliation: Departament de Química Física & CeRQT and Departament de Química Inorgànica & CeRQT, Universitat de Barcelona i Parc Científic de Barcelona, C/ Martí i Franquès 1, E-08028 Barcelona, Spain, and Theoretical Chemistry, Materials Science Centre, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
authors.forename: Ibério de P R
authors.initials: Ide P
authors.lastname: Moreira
authors.affiliation: Departament de Química Física & CeRQT and Departament de Química Inorgànica & CeRQT, Universitat de Barcelona i Parc Científic de Barcelona, C/ Martí i Franquès 1, E-08028 Barcelona, Spain, and Theoretical Chemistry, Materials Science Centre, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
authors.forename: Ramon
authors.initials: R
authors.lastname: Costa
authors.affiliation: Departament de Química Física & CeRQT and Departament de Química Inorgànica & CeRQT, Universitat de Barcelona i Parc Científic de Barcelona, C/ Martí i Franquès 1, E-08028 Barcelona, Spain, and Theoretical Chemistry, Materials Science Centre, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
authors.forename: Michael
authors.initials: M
authors.lastname: Filatov
authors.affiliation: Departament de Química Física & CeRQT and Departament de Química Inorgànica & CeRQT, Universitat de Barcelona i Parc Científic de Barcelona, C/ Martí i Franquès 1, E-08028 Barcelona, Spain, and Theoretical Chemistry, Materials Science Centre, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
authors.forename: Francesc
authors.initials: F
authors.lastname: Illas