Figure 2.

Performance comparisons of different exchange–correlation functionals in predicting the experimentally measured redox potentials, $E_{\exp }^{\mathrm{o}}$. The scatter plots (a–c) show linear correlations of the DFT calculated energy difference, $\mathrm{\Delta }{E}_{\mathrm{rxn}}^{\mathrm{DFT}}$, versus $E_{\exp }^{\mathrm{o}}$, for the three representative functionals of (a) PBE, (b) B3LYP, and (c) M08-HX. The bar plot (d) shows the RMSE for all the functionals considered. The color green represents both OPT and SPE in gas-phase, the color orange represents OPT in gas-phase followed by SPE with SOL, and the color blue represents both OPT and SPE with SOL, as also summarized in a tabular format. In (d), the horizontal dashed green line represents PBE_g (RMSE = 0.072 V, R² = 0.954) benchmark, the horizontal dashed blue line represents PBE_aq (RMSE = 0.053 V, R² = 0.975) benchmark, and the horizontal dashed orange line represents PBE_s (RMSE = 0.051 V, R² = 0.977) benchmark.