Green's function theory for defects in graphene sheets

The presence of defects or impurities in graphene sheets is an important factor in its electronic and magnetic properties. In order to study such effects, we develop a Green's function formalism to calculate the electronic localized sates originated by defects or impurities on a graphene sheet. The equations of motion for the Green's functions are determined in the framework of the tight-binding model. The defects are represented by the absence of carbon atoms on the sheet, while impurities are introduced substitutionaly on the sheet.