In this section we focus on how the geometric performance of DFT methods varies with their amount of exact exchange. For this purpose, we employ the α-PBE hybrid which is built from the PBE functional by replacing the α amount of PBE exchange with the same amount of exact exchange. At α = 0.25, α-PBE becomes PBE0. The mean B2se's GEO values for α-PBE/AVnZ (n={Q,D,T}) are shown in the top panel of Figure (note the log-scale in the y-axis). In terms of the shape of the curves, their ranges, and the position of the minima, AVTZ curve is similar to AVQZ, but very different from the AVDZ. Up to α ∼ 0.3, the mean GEO is lower with AVTZ than with AVDZ. At larger α values (α greater than ∼ 0.3), AVDZ becomes more accurate than AVTZ. This behaviour of α-PBE can be traced back to the geometric performance of HF, given that: (i) α-PBE becomes more similar to HF as α approaches 1, (ii) HF's GEO is much lower with AVDZ than AVTZ. The minima of the AVQZ and AVTZ curves are at α ∼ 0.2, whereas that of the AVDZ curve is expectedly shifted towards larger α (α = 0.36). Around these values we can also find most of the optimal α values for GEO of the individual B2se molecules (see Figure ). For example, more than 70% of the optimal α values within the AVTZ basis set for the individual B2se structure lie in between 0.17 and 0.24. If we look at the mean γ (in place of mean GEO ) as a function of α, the minima are still at about the same α values (see the inset in the top panel of Figure ).