Tang Ao-qing et al. have put forward graph theory method for determining the Huckel molecular orbits and the calculation of energy levels for conjugated molecules. Based on the work of the forerunners, the bond-break rule for determining the molecular orbits is presented in this paper. The general concept of the bond ratio is first introduced. The calculation of orbital coefficients and of energy levels are transformed into a calculation of bond ratio and of energy levels. Following the rules governing bond-breaking established in this paper to break some bonds in the structural diagram of molecules and at the same time modify the Coulomb's integration of atoms, it becomes possible to use a group of mutually independent sub-diagrams to replace the complicated structural diagram of molecules. The secular determinants of each sub-diagram must all equal zero. Thereby series of equations (called series of equations of bond ratio) can be established with the energy level and the bond ratio as the unkowns. When this is solved, the energy level and bond ratio are obtained. Because of the simplicity of the construction of the sub-diagrams, the calculation is greatly simplified when this method is used. Futhermore, this method can be widely applied to all kinds of complicated conjugated molecules. In this paper the authors have gone through some calculations for molecules with heteropoly-radicals.

Key words: CALCULATION, HUCKEL MOLECULAR ORBITAL