An Average-of-Configuration Method for Using Kohn-Sham Density Functional Theory in Modeling Ligand-Field Theory

The Amsterdam Density Functional (ADF) package has been used to constrain Kohn-Sham DFT in such a fashion that a transition from KS-DFT to ligand-field theory in the form of the parametrical dq model is completely well-defined. A relationship is established between the strong-field approximation of the parametrical d2 model for the tetrahedral complexes VCl4- and VBr4- and certain fixed-orbital ADF-computed energies. In this way values for all the parameters of the d2 model may be computed, thus allowing the ADF results to be expressed in terms of a KS-DFT energy matrix that can be diagonalized. This means that the KS-DFT deficiency with regard to computation of nondiagonal elements has been overcome and the KS-DFT eigenenergies have become available through the KS-DFT mimicking of the ligand-field plus repulsion model. By using mutually orthogonal strong-field energy matrices, the mimicking has been further elucidated. The computed values for the empirical parameters of VCl4- and VBr4- are in good agreement with experimental data. The spectrochemical and the nephelauxetic series have been computed by including the remaining halide complexes and the quantitatively special position of F- among the halides corroborated for both series.