It was reported that there is an highly elongated and labile C-C bond in the diamantane-diamantane system, as shown in Fig. . The uncommon long length of the bond is believed to be caused by strong steric effect between the two diamantane moieties, and it is also argued that the dispersion effect between the caged alkanes significantly enhances the bonding strength, thus making the system less prone to spontaneous dissociation. Systems containing unusual interactions like this are well suited for study by energy decomposition analysis. Based on the structure of diamantane-diamantane optimized at M06-2X/6-31G(d,p) level, we carried out sobEDA analysis based on B3LYP-D3(BJ)/6-311+G(2d,p) level, each diamantane is treated as a doublet radical, and spin of electrons is flipped for one of the two although the magnitude of ∆Eels and ∆Eorb in this system is evidently increased, the increase in ∆Exrep is significantly higher, which fully reflects that the steric hindrance effect in the diamantane-diamantane system is particularly significant. Another important point is that the ∆Edc is quite notable in this system. Recall that this dispersion correction term for B3LYP can be simply viewed as representing pure or long-range dispersion interaction, one can conclude that the dispersion effect between the two diamantanes indeed greatly stabilizes the elongated C-C bond. By the way, it only took 6 minutes to finish the present sobEDA analysis on a 96-core server, which demonstrates the high efficiency of the implementation of the sobEDA approach. fluorine with strong electron-withdrawing ability, the region above the center of the ring will show Lewis acidity, which allows the C6F6 to combine with anions. In this example, we use sobEDA to investigate the difference in the interaction strength and nature of C6H6•••Na + and C6F6•••Cl -. Their structures optimized at BHandHLYP/6-311+G(2d,p) level are shown in Fig. , and the sobEDA result is given in Table . From the data it can be seen that the overall interaction of C6H6•••Na + is remarkably stronger than that of C6F6•••Cl -. The secondary reason is that the electrostatic interaction of C6H6•••Na + is modestly larger, while the main reason is that the orbital interaction between C6H6 and Na + is conspicuously more intense, which reflects that the binding between Na + and benzene can cause much more evident charge transfer and electronic polarization phenomena. As for exchange-repulsion and Coulomb correlation, they show about the same magnitude for the interactions in the two systems. When doublet CH is used instead of quartet CH in the sobEDA analysis for acetylene, from the corresponding data in Table one can see that there is a reduction of 40 kcal/mol in the interfragment interaction energy, which is due to the fact that the energy of the doublet CH is 20 kcal/mol lower than that of the quartet state. In addition, the exchange-repulsion term (1299.5 kcal/mol) calculated with doublet CH is significantly larger than that with quartet CH (249.0 kcal/mol), this is because there is a significant overlap between the lone pair electrons of the two doublet CH fragments in their bonding region, thus bringing a huge Pauli repulsion effect. At the same time, the ∆Eorb term -1065.9 kcal/mol obtained with doublet CH is also significantly more negative than the counterpart (-336.8 kcal/mol) with quartet CH, clearly the significantly stronger orbital relaxation effect greatly cancels out the oversized exchange-repulsion effect. The analysis conclusion of sobEDA in this example is fully consistent with common chemical knowledge. (HC) -2 (CH) -235.9 -448.9 1299.5 -1065.9 -20.7