code: def set_group_bond(self, atom_index_one, atom_index_two, bond_order):
          
          self.current_group.bond_atom_list.append(atom_index_one)
          self.current_group.bond_atom_list.append(atom_index_two)
          self.current_group.bond_order_list.append(bond_order)
docs: Add bonds within a group.
          :param atom_index_one: the integer atom index (in the group) of the first partner in the bond
          :param atom_index_two: the integer atom index (in the group) of the second partner in the bond
          :param bond_order: the integer bond order