Multi-Electronic Orbitals in the Crystal Field

However, the multi-electronic treatment brings in an additional effect the field applied to an electron by the other electrons from the multi-electrons orbitals. 

Therefore, in order to satisfy the Pauli principle of the orbital occupancies, for the multi-electrons orbitals in the crystal field there appears two effects of electronic repelling  

Therefore, the consideration of the multi-electronic treatment of the resulting terms depending on the relation Dq/B between these factors appears as natural next step. 

For the case Dq B one has the situation of the strong crystal field, but in relation with B, because Dq still remains as a perturbation On the contrary, the case Dq B is treated as the weak crystal field. 

The practical difference in considering these cases is the order in which the two influences are considered firstly the strong one and subsequently the weak one. 

---