The most interesting feature of OX-B3LYP is the very low value of the range separation parameter (ω = 0.025 a0 -1 ). This can be understood by noting that 1/ω roughly corresponds to the distance at which electron-electron interactions are no longer screened (when EE∞ = 100%). In general-purpose rangeseparated DFAs such as the original LC-ωPBE (ω = 0.47 a0 -1 , grey in Figure ), 1/ω is comparable to the length of a single bond (1/ω = 1.1 Å). In the LC-ωPBE variant suitable for singlylinked porphyrins (ω = 0.1 a0 -1 ), 1/ω is on the order of a single porphyrin (5.3 Å), indicating that electrons are strongly delocalized within each porphyrin, but that inter-porphyrin interactions are unscreened. In OX-B3LYP (dark blue in Figure ) screening persists up to several porphyrins in length (1/ω = 21.2 Å), reflecting strong inter-porphyrin coupling in c-PN nanobelts. An alternative non-empirical approach for tuning a DFA for a specific system relies on making it compliant with Koopmans' theorem, which is usually accomplished by varying ω to match the negative HOMO energy and the vertical electron detachment energy of the neutral molecule. Applying this procedure to c-P6, we obtain ω = 0.030 a0 -1 as the optimal value, which is very close to the ω = 0.025 a0 -1 in OX-B3LYP (see SI Section C). Therefore, two unrelated non-empirical tuning procedures, based on the minimization of coupled clusters energy or compliance to Koopmans' theorem, independently produce very similar estimates for the limit of global aromaticity. Finally, thermal movement does not appear to damp the ring current (see SI Section D).