code: public static double predictIP(IAtomContainer container, IAtom atom) throws CDKException {
          double value = 0;
  
          // at least one lone pair orbital is necessary to ionize
          if (container.getConnectedLonePairsCount(atom) == 0) return value;
  
          // control if the IAtom belongs in some family
          if (familyHalogen(atom))
              value = getDTHalogenF(getQSARs(container, atom));
          else if (familyOxygen(atom))
              value = getDTOxygenF(getQSARs(container, atom));
          else if (familyNitrogen(atom)) value = getDTNitrogenF(getQSARs(container, atom));
  
          return value;
      }
docs: Method which is predict the Ionization Potential from given atom.
  
  @param container The IAtomContainer where is contained the IAtom
  @param atom      The IAtom to prediction the IP
  @return          The value in eV