title: Ab Initio CI Determination of the Exchange Coupling Constant of Doubly-Bridged Nickel(II) Dimers.
abstract: Ab initio DDCI2 (difference-dedicated configuration interaction) calculations are performed on the exchange coupling constant of the doubly-bridged Ni(II) complexes [Ni(en)(2)Cl](2)(2+) and [Ni(terpy)(N(3))](2)(2+), which are modeled by substituting the external ligands with ammonia groups. The variational CI space is selected on the grounds of the effective Hamiltonian theory and includes all the second-order contributions to the difference between the lowest quintet, triplet, and singlet states. Both complexes are found to be ferromagnetic, with coupling constants of 1.8 and 21.1 cm(-1), in good agreement with the experiment. A transformation of the molecular orbitals is also proposed for large systems, enabling the molecular orbital set to be significantly truncated-as well as the file of two-electron integrals and the DDCI2 space-with no loss of efficiency.
authors.affiliation: Departament de Química, Universitat Rovira i Virgili, Pl. Imperial Tarraco 1, 43005 Tarragona, Spain, and Laboratoire de Physique Quantique, URA 505, IRSAMC, Université Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex, France.
authors.forename: O.
authors.initials: O
authors.lastname: Castell
authors.forename: R.
authors.initials: R
authors.lastname: Caballol
authors.forename: V. M.
authors.initials: VM
authors.lastname: García
authors.forename: K.
authors.initials: K
authors.lastname: Handrick