A comment on “The interaction of X 2 (X = F, Cl, and Br) with active sites of graphite” [Xu et al., Chem. Phys. Lett., 418, 413 (2006)]

A comment on "The interaction of X2 (X = F, Cl, and Br) with active sites of graphite" [Xu et al., Chem. Abstract In their article, Xu et al. [1] present the adsorption energies for the chemisorption of the three halogens F 2, Cl 2, and Br 2 on the active sites of graphite. The three investigated systems are the three most stable surfaces, (001), (100), and (110); the latter two are also called zigzag and armchair surface, respectively. Due to some inconsistencies in their article, we re-evaluated the results of Xu et al. in order to investigate the impact on the adsorption energies of the halogens. For the (001) surface, our results agree with Xu et al. However, for the other two surfaces, we find major differences. Contrary to Xu et al., we find that the halogens adsorb the strongest on the zigzag surface. The second strongest adsorption is found on the armchair surface for the symmetric configurations, the third strongest for the asymmetric configurations. Several reasons are given which explain this discrepancy. The most striking source of error in the work of Xu et al. is due to the fact that they did not choose the correct spin multiplicities for the model systems which means that they performed the calculations in excited states. This leads to errors between 50-600% for the zigzag surface and 3-42% for the armchair surface.