code: def get_extended_surface_mesh(self, repeat=(5, 5, 1)):
          
          surf_str = Structure.from_sites(self.surface_sites)
          surf_str.make_supercell(repeat)
          return surf_str
docs: Gets an extended surface mesh for to use for adsorption
          site finding by constructing supercell of surface sites
  
          Args:
              repeat (3-tuple): repeat for getting extended surface mesh