Hydrogenation and Fluorination of Graphene Models: Analysis via the Average Local Ionization Energy

We have investigated the use of the average local ionization energy, I?(S)(r), as a means for rapidly predicting the relative reactivities of different sites on two model graphene surfaces toward the successive addition of one, two, and three hydrogen or fluorine atoms. The I?(S)(r) results were compared with directly computed interaction energies, at the B3LYP/6-311G(d,p) level. I?(S)(r) correctly predicts that the edges of graphene sheets are more reactive than the interior portions. It shows that added hydrogens activate the adjoining (ortho) sites and deactivate those that are separated by one site (meta). Overall, I?(S)(r) is effective for rapidly (single calculations) estimating the relative site reactivities of these large systems, although it reflects only the system prior to an interaction and cannot take into account postinteraction factors, e.g., structural distortion.