Correlation-bound anion states

In a correlation-bound anion, the excess electron is bound to the molecule in a diffuse non-valence orbital and electron correlation is crucial for the electron binding. Examples of such anions include Xe$_{\mathrm{n}}^{\mathrm{-}}$ clusters and certain (H$_{\mathrm{2}}$O)$_{\mathrm{n}}^{\mathrm{-}}$ clusters. Using many-body methods we have characterized correlation-bound anion states of C$_{\mathrm{60}}$, C$_{\mathrm{6}}$F$_{\mathrm{6}}$ and several large acenes. The correlation-bound anion states of these species are related to the image potential states of graphene. Modeling correlation-bound anion states presents challenges for \textit{ab initio }approaches. Hartree-Fock based approaches such as MP2 and CCSD fail to describe these states. The key to treating these species theoretically is to employ a method that allows the singly occupied orbital to relax in the presence of the long-range correlation effects. A model potential approach accounting for image effects for describing the binding of the excess electron will be presented for C$_{\mathrm{60}}$.