code: def set_charge_and_spin(self, charge, spin_multiplicity=None):
          
          self._charge = charge
          nelectrons = 0
          for site in self._sites:
              for sp, amt in site.species.items():
                  if not isinstance(sp, DummySpecie):
                      nelectrons += sp.Z * amt
          nelectrons -= charge
          self._nelectrons = nelectrons
          if spin_multiplicity:
              if (nelectrons + spin_multiplicity) % 2 != 1:
                  raise ValueError(
                      "Charge of {} and spin multiplicity of {} is"
                      " not possible for this molecule".format(
                          self._charge, spin_multiplicity))
              self._spin_multiplicity = spin_multiplicity
          else:
              self._spin_multiplicity = 1 if nelectrons % 2 == 0 else 2
docs: Set the charge and spin multiplicity.
  
          Args:
              charge (int): Charge for the molecule. Defaults to 0.
              spin_multiplicity (int): Spin multiplicity for molecule.
                  Defaults to None, which means that the spin multiplicity is
                  set to 1 if the molecule has no unpaired electrons and to 2
                  if there are unpaired electrons.