Weak covalency in transition metal salts

A theory of weak covalency effects in transition metal salts based upon a configuration interaction approach is discussed. The configuration interaction scheme is compared and contrasted with the more usual molecular orbital or Hartree-Fock approach and shown to include important correlation effects omitted in the latter. The method is applied to calculate some properties (transferred hyperfine interaction effects and cubic crystal field parameters) of the salts KN1F 3 and KMnF 3 and shown to give a reasonably good account of the magnitudes of these effects. In particular, the effect of the half-closed d shell of Mn 2+ , the role played by 4s electrons and the contribution of terms of higher order in the covalency parameters are investigated.