Adsorption of gaseous species, and in particular of hydrogen atoms, on graphene is an important process for the chemistry of this material. At the equilibrium geometry, the H atom is covalently bonded to a carbon that puckers out from the surface plane. Nevertheless the \emph{flat} graphene geometry becomes important when considering the full sticking dynamics. Here we show how GGA-DFT predicts a wrong spin state for this geometry, namely Sz=0 for a single H atom on graphene. We show how this is caused by the self-interaction error since the system shows fractional electron occupations in the two bands closest to the Fermi energy. It is demonstrated how the use of hybrid functionals or the GGA+U method an be used to retrieve the correct spin solution although the latter gives an incorrect potential energy curve.
@article{arxiv.1002.4117,
title = {Role of the self-interaction error in studying chemisorption on graphene from first-principles},
author = {Simone Casolo and Espen Flage-Larsen and Ole Martin Løvvik and George R. Darling and Gian Franco Tantardini},
journal= {arXiv preprint arXiv:1002.4117},
year = {2015}
}