On the Theory of the d‐Electron Covalency in Ionic Crystals

The method of calculating the covalency parameter λ is examined, with reference to the unrestricted Hartree‐Fock method. The results of the calculations carried out for the (NiF6)4− complex indicate that the unrestricted Hartree‐Fock method leads to considerably smaller values of λ than the method of maximizing the antibonding orbital energy used by Sugano and Shulman [3]. An approximate treatment of the self‐consistency is proposed, introducing delocalization of the σ‐orbitals into the one‐electron Hamiltonian. The modifications introduced by this treatment are especially significant in the method used in [3].