  Energetic and geometric aspects of the permeation of low-Z atoms through
graphene sheets are investigated. Energy barriers and deformations are
calculated via density functional theory for the permeation of H, He, Li and Be
atoms at several surface sites and at a hollow site for atoms B, C, O and Ne
atoms. Graphene is modeled by large planar polycyclic aromatic hydrocarbons and
the convergence of both energy barriers and deformation curves with increasing
size of these hydrocarbons is investigated. Effective energy curves are
summarized for the atoms under consideration in three different interaction
regimes realized different geometrical constraints. In addition to the bare
graphene model, the interaction between low-Z atoms and 100% hydrogenated
coronene as a model for graphane is also investigated. The adiabatic barriers
range from about 5 eV (1 eV = 1.602 x 10-19 J) for H to about 20 eV for Ne.
Facilitation of the permeation by temporary chemical bonding is observed for O
and C and for B and Be when interacting with hydrogenated coronene. The results
are in good agreement with existing experimental and theoretical work and
reflect the essential physics of the dynamics of H bombardment of graphite
(0001) surfaces. Implications for modeling chemical sputtering of graphite in a
mixed-material scenario as it will be the case in the next step fusion
experiment ITER and potential building are discussed.
