In this work density functional theory (DFT) and diffusion Monte Carlo (DMC) methods are used to calculate the binding energy of a H atom chemisorbed on the graphene surface. The Perdew-Burke-Ernzerhof (PBE) value of the binding energy is about 20% larger in magnitude than the diffusion Monte Carlo result. The inclusion of exact exchange through the use of the Heyd-Scuseria-Ernzerhof (HSE) functional brings the DFT value of the binding energy closer in line with the DMC result. It is also found that there are significant differences in the charge distributions determined using PBE and DMC approaches. Comment: The following article has been submitted to The Journal of Chemical Physics
