First-principles study of electronic properties of hydrogenated graphite

Progressive implantation of hydrogen atoms into graphite is modeled by first-principles density functional theory. The maximum $\mathrm{H}∕\mathrm{C}$ ratio was found at 53%, which is in good agreement with experimental results. The hydrogen trapping energy varies from $\ensuremath{-}0.7\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ at very low concentrations to a limit of $\ensuremath{-}1.9\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ at saturation. Special attention is given to the electronic density of states at each step of the process; they are compared to the experimental spectra from electron spectroscopy on graphite hydrogenated by energetic ions bombardment. The density of states of the fully hydrogenated graphite is compared to that of diamond. Step-by-step study of the ${\ensuremath{\pi}}^{*}$ density of states starting from pure graphite (all $s{p}^{2}$ carbon) leads to a criterion of characterization of graphitic materials amorphization. The calculated $s{p}^{3}∕s{p}^{2}$ ratio in hydrogenated graphite is proposed as a model to quantify the rate of tetrahedral carbon atoms in amorphous and hydrogenated amorphous carbon samples.