Modeling of hydrogen and hydroxyl group migration on graphene.

Density functional calculations of optimized geometries for the migration of single hydrogen and hydroxyl groups on graphene are performed. It is shown that the migration energy barrier for the hydroxyl group is three times larger than for hydrogen. The crucial role of supercell size for the values of the migration barriers is discussed. The paired migration of hydrogen and hydroxyl groups has also been examined. It could be concluded that hydroxyl group based magnetism is rather stable in contrast with unstable hydrogen based magnetism of functionalized graphene. The role of water in the migration of hydroxyl groups is also discussed, with the results of the calculations predicting that the presence of water weakens the covalent bonds and makes these groups more fluid. Increasing the number of water molecules associated with hydroxyl groups provides an increase of the migration energy.