Doublet open-shell ground states

However, in octahedral Cr(III) complexes, Cr3+ is a d3 metal ion with three electrons in the HOMO orbitals ttM (t ). Thus the complexes of Cr(III) have an open-shell ground-state configuration, which on excitation produces quartet and doublet states (Figure 1.13). 

The SCF orbitals of open-shell systems may be obtained by the (spin) unrestricted Hartree-Fock (UHF) open-shell approach of Pople and Nes-bet (1954). In this method, the orbitals associated with an a spin function are different from those associated with a j8 spin function. So, for a doublet ground state In + 1 electrons), the wave function is written as ... 

For a closed-shell molecule, the primary accessible ion states correspond with holes in the occupied valence orbitals of the molecule. However, if a molecule has an open-shell configuration, exchange splitting often causes this simple correlation to break down. For example, if a molecule were to have a configuration, a doublet ground state... 

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