Self-Interaction Correction Studies of the Caged Electron Acceptor: Perfluorocubane (C₈F₈)

Recently, Sugiyama et al. reported the complete fluorination of cubane (C₈H₈) to produce perfluorocubane (C₈F₈), which acts as an electron acceptor to form the perfluorocubane radical anion (C₈F₈⁻). Their experimental and theoretical analysis concluded that the unpaired electron in C₈F₈⁻ resides inside the carbon cage. Motivated by this, we analyze C₈F₈⁻ in this study to examine its spin density and electron affinity. It is well-known that the self-interaction error (SIE) causes inaccuracies in describing anionic systems. In the standard semi-local and global hybrid density functional approximations, positive orbital energies indicate unbound electrons thus leading to delocalization error and systematic errors in calculating the vertical detachment energy (VDE). We explore how SIE affects density functional approximations across the three lowest rungs of Jacob’s ladder (e.g., LSDA, PBE, and the recent SCAN family of meta-GGA functionals) in computing the spin density and electron affinities of C₈F₈⁻. To do this, we utilize self-interaction correction (SIC) methods which include the Perdew-Zunger approach and local scaling methods. Our main goal is to understand how these corrections influence the description of C₈F₈⁻, especially regarding the impact of SIC on its spin density and electron affinity. We also estimate the VDE from the absolute value of the highest occupied eigenvalues to assess the ability of C₈F₈⁻ to act as a strong electron acceptor.

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