title: Calculation of zero-field splitting parameters: comparison of a two-component noncolinear spin-density-functional method and a one-component perturbational approach.
abstract: Two different sets of approaches for the density-functional calculation of the spin-orbit contributions to zero-field splitting (ZFS) parameters of high-spin systems have been implemented within the same quantum chemistry code ReSpect and have been validated and compared for a series of model systems. The first approach includes spin-orbit coupling variationally in a two-component calculation, using either an all-electron Douglas-Kroll-Hess ansatz or two-component relativistic pseudopotentials. The ZFS parameters are computed directly from energy differences between different relativistic states. Additionally, an approximate second-order perturbation theory approach has been implemented, based on nonrelativistic or scalar relativistic wave functions. For a series of group 16 triplet diatomics and for the octet GdH3 molecules, two-component density functional calculations underestimate the zero-field splitting D systematically by a factor of 2. This may be rationalized readily by the incomplete description of states with absolute value MJ < J by a single-determinantal wave function built from two-component spinors. In the case of two 3d transition metal complexes and for GdH3, the results depend furthermore sensitively on exchange-correlation functional. Results of the alternative one-component approach agree strikingly with the two-component data for systems with small spin-orbit effects and start to deviate from them only for heavier systems with large spin-orbit effects. These results have fundamental implications for the achievable accuracy of one-component density-functional approaches used widely to compute ZFS parameters in the field of molecular magnetism. Possible refinements of both one-and two-component approaches are discussed.
authors.affiliation: Institut für Anorganische Chemie, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany.
authors.forename: Roman
authors.initials: R
authors.lastname: Reviakine
authors.forename: Alexei V
authors.initials: AV
authors.lastname: Arbuznikov
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Tremblay
authors.forename: Christian
authors.initials: C
authors.lastname: Remenyi
authors.forename: Olga L
authors.initials: OL
authors.lastname: Malkina
authors.forename: Vladimir G
authors.initials: VG
authors.lastname: Malkin
authors.forename: Martin
authors.initials: M
authors.lastname: Kaupp