In other words, even if we would use the exact DFT XC functional in the response equations, it would be an approximate functional for TDDFT, since it would only depend on the instantaneous density. In fact, Dreuw and Head-Gordon showed that the errors of TDDFT are coming from both the orbital energies of SCF and response calculations. By individually tuning XC functionals for the two steps, we demonstrated that one can obtain better XC functionals for response theories.