A combined density functional and coupled-cluster theory study on correlation-bound anions of perfluorinated compounds

Perfluorinated cage molecules are hypothesized to have excellent electron-capture abilities, since they have the capacity to host an electron inside the carbon framework. The formed anions have been characterized as correlation-bound, meaning that they are unbound at the Hartree-Fock level. In this study, we assess the performance of density functional and coupled-cluster theory in the calculation of electron affinities of perfluorotetrahedrane, perfluorocubane, perfluoroadamantane and perfluorobenzene. We also characterize the anionic states using the electronic Fukui function and the electron localization function and investigate geometry changes upon electron attachment. To this end, the charge stabilization method is used for describing both the energy and spatial functions of metastable anionic states whenever they occur, and special attention is paid to how the electronic Fukui function and electron localization function differ for unbound anions compared to bound anions. For valence anions, density functional theory turns out to perform at a similar level as spin-scaled versions of second-order approximate coupled cluster singles and doubles theory, but it is not as accurate for describing correlation-bound anions. Only for the largest considered cage molecule, perfluoroadamantane, we found evidence for electron capture inside the cage, and this was only before the molecular geometry was allowed to relax. For anions that are described as metastable, the localization inside the cage became less pronounced.