At the dissociation limit, an exact singlet and triplet mixing (⟨S 2 ⟩ = 1) occurs in the U-SF-TDDFT. Since the interaction between the two separated electrons becomes nearly zero at this limit, the singlet and triplet states become energetically degenerate. Consequently, despite the exact singlet and triplet mixing, the final system energy of the U-SF-TDDFT is exactly identical to that of the UMRSF.