In 1996, Bauernschmitt et al. employed TD-DFT to compute the first four electronic excitations of PP to validate exchange correlation functionals, including the local density approximation (LDA: S-VWN), the generalized gradient approximation (GGA: BP86) and hybrid functional (B3LYP). Their results showed that TD-DFT excitation using the BP86 functional are in better accordance with experiment than CIS and TD-HF. Also, CASPT2 possesses an error of more than 0.3 eV for the Q-bands compared to experimental results. However, the employed basis set was overall small for post-HF approaches.