We also plotted the ELF function for π out -and π in -systems (respectively abbreviated as ELF-π out and ELF-π in ) of C 18 Br 6 , which has different chemical meaning from the LOL function but can also describe the electron delocalization in molecular skeleton, as shown in Figure . Both the isosurfaces and the color-fill maps of ELF-π point to the same conclusion as given by the LOL-π analysis. The difference is that ELF isosurfaces are much wider and appear bloated compared to the cases of LOL, which is just conducive to the quantitative bifurcation analysis. The bifurcation values of long C-C bonds in C 18 Br 6 are calculated to be no more than 0.55 and 0.45 for ELF-π out and ELF-π in , respectively. The corresponding values of C 18 at the same calculation level are all around 0.55, showing that the strength of π in -electron delocalizations in C 18 Br 6 is significantly weaker than that in C 18 , but their π out -delocalizations are similar. AV1245 is a reliable method for quantifying the degree of electron delocalization on a specific path. We have applied it to the studies of C 18 and its cyclocarbon oxide precursors, C 18 (CO) n (n = 2, 4, and 6), and gained useful insights. The AV1245 values for π out -and π in -electrons of C 18 Br 6 over the path consisting of 18 carbon atoms were calculated to be 1.90 and -0.26, respectively. The relatively large AV1245 value of π out -electrons indicates a notable π out -electron delocalization effect over the carbon ring, while the small value for π in -electrons implies the extent of π in -global delocalization is negligible. The AV1245 results fully confirmed the above assertions about the electron delocalization of the C 18 Br 6 .