Variation of superexchange with interatomic distance. I. TheT2gsystemV++-F−-V++

The configuration-interaction method is applied to calculate the superexchange in ${\mathrm{V}}^{++}$-${\mathrm{F}}^{-}$-${\mathrm{V}}^{++}$ system as a function of interatomic distance. It is found that $\frac{\partial \ln J}{\partial \ln R}\simeq 12$ for small variations of the interatomic spacing about an equilibrium ${\mathrm{V}}^{++}$-${\mathrm{F}}^{-}$ separation of 2 Å. This may be characteristic of those systems with ground states which transform as the $T_{2g}$ irreducible representation of the octahedral group and admit, therefore, of only $d\left(t_{2g}\right)-p_{\pi }$ cation-anion bonding.