Correlated Electronic Properties of a Graphene Nanoflake: Coronene

We report studies of the correlated excited states of coronene and substituted coronene within the Pariser-Parr-Pople (PPP) correlated $\pi$-electron model employing symmetry adapted density matrix renormalization group technique. These polynuclear aromatic hydrocarbons can be considered as graphene nanoflakes. We review their electronic structures utilizing a new symmetry adaptation scheme that exploits electron-hole symmetry, spin-inversion symmetry and end-to-end interchange symmetry. Study of the electronic structures sheds light on the electron correlation effects in these finite-size graphene analogues, which diminishes on going from one-dimensional to higher-dimensional systems, yet is significant within these finite graphene derivatives.