code: def nonstoichiometric_symmetrized_slab(self, init_slab, tol=1e-3):
  
          
  
          sg = SpacegroupAnalyzer(init_slab, symprec=tol)
  
          if sg.is_laue():
              return [init_slab]
  
          nonstoich_slabs = []
          # Build an equivalent surface slab for each of the different surfaces
          for top in [True, False]:
              asym = True
              slab = init_slab.copy()
              slab.energy = init_slab.energy
  
              while asym:
                  # Keep removing sites from the bottom one by one until both
                  # surfaces are symmetric or the number of sites removed has
                  # exceeded 10 percent of the original slab
  
                  c_dir = [site[2] for i, site in enumerate(slab.frac_coords)]
  
                  if top:
                      slab.remove_sites([c_dir.index(max(c_dir))])
                  else:
                      slab.remove_sites([c_dir.index(min(c_dir))])
                  if len(slab) <= len(self.parent):
                      break
  
                  # Check if the altered surface is symmetric
                  sg = SpacegroupAnalyzer(slab, symprec=tol)
                  if sg.is_laue():
                      asym = False
                      nonstoich_slabs.append(slab)
  
          if len(slab) <= len(self.parent):
              warnings.warn("Too many sites removed, please use a larger slab "
                            "size.")
  
          return nonstoich_slabs
docs: This method checks whether or not the two surfaces of the slab are
          equivalent. If the point group of the slab has an inversion symmetry (
          ie. belong to one of the Laue groups), then it is assumed that the
          surfaces should be equivalent. Otherwise, sites at the bottom of the
          slab will be removed until the slab is symmetric. Note the removal of sites
          can destroy the stoichiometry of the slab. For non-elemental
          structures, the chemical potential will be needed to calculate surface energy.
  
          Arg:
              init_slab (Structure): A single slab structure
              tol (float): Tolerance for SpaceGroupanalyzer.
  
          Returns:
              Slab (structure): A symmetrized Slab object.