d-d spectra of transition metal oxides by effective crystal field method

The effective crystal field (ECF) method is applied to d-d excitations in metal oxides of the first transition series as measured by optical and EELS techniques. The computations are performed in the framework of the cluster approximation. The octahedral clusters are employed to simulate the transition metal ions in the bulk, the square pyramidal ones for simulation of the ions on the (100) crystal surfaces. A fair agreement between the calculation performed without additional parameter adjustment and experiment is reached when the effect of the Madelung potential on the electronic structure of the oxygens surrounding the transition metal ion and by this on the effective crystal field induced by them is carefully taken into account.