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 (delta), electron affinity (EA), and the inversion barriers to the ring-puckering (Delta E-RP) of c-C4F80,- and the trans-to-cis isomerization (Delta E-iso) of 2-C4F80,-. It was shown that reliable calculations of the EAs of the PFCs require that at least one set off functions be added to the split valence-shell type and diffuse basis functions. Our analysis of the calculated values recommends the omega B97X-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-C4F8- systems revealed that the transition state of the neutral form (TSiso) is symmetric but that its anionic counterpart (TSiso-) is asymmetric in both geometry and charge distribution. This asymmetry corresponds to a kind of electronic charge flow from one side of 2-C4F8- 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. (C) 2013 Elsevier B.V. All rights reserved.