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 paper, we assess the performance of Hartree-Fock theory, density functional and coupled-cluster methods for 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, use is made of the charge stabilization method for describing metastable anionic states whenever they occur. Hartree-Fock theory indeed fails to describe attachment and detachment energies correctly and leads to inaccuracies in the obtained electron densities. For valence anions, density functional theory turns out to perform at a similar level as spin-scaled versions of the second-order approximate coupled cluster singles and doubles theory with the resolution-of-the-identity, but 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 only before the molecular geometry was allowed to relax. For anions that are described as metastable, the localization inside the cage became less pronounced.