Density functional theory calculations for simple prototypes of perfluorocarbons: neutral and anionic c-C4F8 and 2-C4F8

In order to find a density functional theory (DFT) method appropriate to perfluorocarbon molecules (PFCs), the properties of three isomeric forms of C4F8 were calculated, with special emphasis on the ring-puckering angle (δ), electron affinity (EA), and the inversion barriers to the ring-puckering (ΔERP) of c -C 4 F 8 0 , − and the trans-to-cis isomerization (ΔEiso) of 2-C 4 F 8 0 , − . It was shown that reliable calculations of the EAs of the PFCs require that at least one set of f functions be added to the split valence-shell type and diffuse basis functions. Our analysis of the calculated values recommends the ωB97X-D/aVTZ method for future studies of other PFC systems. Examination of the trans-to-cis isomerization of the neutral 2-C4F8 and anionic 2-C 4 F 8 − systems revealed that the transition state of the neutral form (TSiso) is symmetric but that its anionic counterpart ( T S iso − ) is asymmetric in both geometry and charge distribution. This asymmetry corresponds to a kind of electronic charge flow from one side of 2-C 4 F 8 − to the other. The reason for the lower energy barrier of the isomerization of the anion than that of the neutral form is also discussed.