  The formation energies for mono- and bivacancies in graphene in the presence
of adatoms of various metals and small metallic clusters have been calculated.
It is shown that transition metal impurities, such as iron, nickel and,
especially, cobalt reduce dramatically the vacancy formation energies whereas
gold impurities have almost no effect on characteristics of the vacancies. This
results highlight that special measures are required in order to protect
graphene from damage by transition metal leads.
