code: public static double evalSimpleIndex(IAtomContainer atomContainer, List<List<Integer>> fragLists) {
          double sum = 0;
          for (List<Integer> fragList : fragLists) {
              double prod = 1.0;
              for (Integer atomSerial : fragList) {
                  IAtom atom = atomContainer.getAtom(atomSerial);
                  int nconnected = atomContainer.getConnectedBondsCount(atom);
                  prod = prod * nconnected;
              }
              if (prod != 0) sum += 1.0 / Math.sqrt(prod);
          }
          return sum;
      }
docs: Evaluates the simple chi index for a set of fragments.
  
  @param atomContainer The target <code>AtomContainer</code>
  @param fragLists      A list of fragments
  @return The simple chi index