Density functional study of adsorption of molecular hydrogen on graphene layers

Density functional theory has been used to study the adsorption of molecular ${\mathrm{H}}_{\mathrm{2}}$ on a graphene layer. Different adsorption sites on top of atoms, bonds and the center of carbon hexagons have been considered and compared. We conclude that the most stable configuration of ${\mathrm{H}}_{\mathrm{2}}$ is physisorbed above the center of a hexagon. Barriers for classical diffusion are, however, very small.