Unlike ROKS, now the spatial parts of α (black) and β (green) orbitals are different in UKS. It should be noted that the spatial part of α (black) orbitals of M S = +1 state is identical to the β (black) orbitals of M S = -1 and vise versa. To be consistent, the black and green spatial orbitals are designated as χ and χ, respectively as shown in Fig. .