Reduces the set of adsorbate sites by finding removing
        symmetrically equivalent duplicates

        Args:
            coords_set: coordinate set in cartesian coordinates
            threshold: tolerance for distance equivalence, used
                as input to in_coord_list_pbc for dupl. checking

def symm_reduce(self, coords_set, threshold=1e-6):
        """
        Reduces the set of adsorbate sites by finding removing
        symmetrically equivalent duplicates

        Args:
            coords_set: coordinate set in cartesian coordinates
            threshold: tolerance for distance equivalence, used
                as input to in_coord_list_pbc for dupl. checking
        """
        surf_sg = SpacegroupAnalyzer(self.slab, 0.1)
        symm_ops = surf_sg.get_symmetry_operations()
        unique_coords = []
        # Convert to fractional
        coords_set = [self.slab.lattice.get_fractional_coords(coords)
                      for coords in coords_set]
        for coords in coords_set:
            incoord = False
            for op in symm_ops:
                if in_coord_list_pbc(unique_coords, op.operate(coords),
                                     atol=threshold):
                    incoord = True
                    break
            if not incoord:
                unique_coords += [coords]
        # convert back to cartesian
        return [self.slab.lattice.get_cartesian_coords(coords)
                for coords in unique_coords]