Covalency in Ionic Crystals: KNiF3

Within the framework of the self-consistent field molecular orbital theory, studies are made of the covalency and the cubic field splitting parameter in ionic crystals, with a particular reference to KNiF 3 . It is pointed out that the effect of the rearrangement among the virtually transfered electron and d -electrons is essential in obtaining proper values of the covalency. By using the Heitler-London theory with an admixed excited configuration, in which atomic orbitals of the metal and ligand ions are different from those in the ground configuration, this effect of the rearrangement can be taken into account to some extent, and a reasonable value of the covalency may be obtained. Finally, by making a one to one correspondence between the expressions in the generalized Heitler-London theory and a simple molecular orbial theory, it is shown that the simple molecular orbital theory could successfully be used if an appropriate effective Hamiltonian is assumed.