Stable hydrogen configurations between graphite layers

Based on the density functional theory, we investigate and discuss what possible stable configurations hydrogen might assume, once found inside/between graphite layers stacked in an AB configuration. Our calculation results show that the reconstruction of the constituent carbon atoms is crucial in determining the final configuration of hydrogen. When a hydrogen atom impinges directly above one of the carbon atoms on the surface, that carbon atom relaxes 0.26-0.33 Angstrom towards the incoming hydrogen atom. Similarly, when a hydrogen atom is positioned between two graphite layers such that there are carbon atoms immediately above and below it, one of these two carbon atoms relaxes 0.26-0.33 A towards the hydrogen atom, while the other carbon atom hardly moves. The hydrogen atom finally takes a position 1.11-1.15 Angstrom from one of the carbon atoms and 1.87-1.98 Angstrom from the other. Note that, without the hydrogen atom, the distance between successive layers is 3.35 Angstrom. Our calculation results indicate agreement with the results of recent neutron diffraction and thermal desorption studies on deuterated nanographite. Our calculation results also suggest that, due to the reconstruction of the carbon atoms, it is more likely to find hydrogen as atomic hydrogen rather than as molecular hydrogen between the graphite layers.