The right side of Figure compares these two approaches to random selection among the active spaces generated with different values of λ. The figure shows that tPBE distinguishes robustly between qualitatively accurate and inaccurate complete-active-space wave functions (i.e., there are no very large erros), while CASCI does little better than random chance, which does very poorly. The mean absolute error of the tPBE0 excitation energies is 1.24 eV with CASCI used for selection, as compared to 0.19 eV with tPBE used for selection. Furthermore, the maximum absolute error decreases from 3.61 eV with CASCI selection to 0.63 eV with tPBE selection. As a hybrid between tPBE and CASCI, selection with tPBE0 performs midway between these two approaches.