Calculation of spin-orbit coupling within the LFDFT:: Applications to [NiX4]2- (X=F-, Cl-, Br-, I-)

Spin-orbit coupling has been introduced into our newly developed ligand field density functional theory (LFDFT), using the zero-order regular approximation as implemented into the Amsterdam density functional (ADF) code. Application of the formalism to a series of NiX42- (X=F-, Cl-, Br-, I-) compounds shows the increasing importance of intra-ligand spin-orbit coupling across the F, Cl, Br, I series, to lead to sign reversal (in the case of Brand I-) of the spin-orbit splitting within the t(2)-orbitals manifold of Ni2+. Symmetry lowering from T-d to D-2d, due to the Jahn-Teller coupling for the e(4)t(2)(4) configuration of NiX42-, is used to manifest further the effect of bonding changes on the sign and magnitude of the spin-orbit constant. Ligand field and spin-orbit coupling matrices are found to be correlated, with the higher erxtent of antibonding being accompanied by lower values of the spin-orbit coupling constant. In cases of little or no symmetry, this leads to situations in which ligand field and spin-orbit coupling cannot be neatly separated in the mathematical description. Using these results, the electronic energy levels of this series of compounds are predicted to be in good agreement with available spectral and magnetic data from literature. (C) 2004 Wiley Periodicals, Inc.