Role of the self-interaction error in studying chemisorption on graphene from first-principles

TL;DR

This paper investigates how the self-interaction error in GGA-DFT affects the predicted spin state of hydrogen chemisorption on graphene, highlighting the importance of using hybrid functionals or GGA+U for accurate results.

Contribution

It demonstrates that self-interaction error causes incorrect spin states in GGA-DFT calculations of hydrogen on graphene and shows how hybrid functionals or GGA+U can correct this.

Findings

GGA-DFT predicts a wrong spin state ($S_z$=0) for H on graphene.

Self-interaction error causes fractional electron occupations near the Fermi level.

Hybrid functionals and GGA+U can recover the correct spin state, but GGA+U may give an inaccurate potential energy curve.

Abstract

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 $S_z$=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.