fullerenes, but the small size of the carbon ring hinders the close contact between fullerenes, resulting in a dmin of up to 4.86 Å, which is obviously much longer than the sum of the vdW radius of the two carbons (~ 3.40 Å). As the ring size increases to C22, there is not only a significant C60…C22 interaction, but also an obvious interaction between two C60 fullerenes in the 2C60@C22, as shown by the yellow isosurface and small dmin. With the complex comes to 2C60@C26, although the C60…C60 interaction is further enhanced, as shown by the yellow isosurface becoming wider and dmin decreasing to 3.05 Å, the interaction between cyclocarbon and fullerene is weakened to a certain extent, which is vividly reflected by the narrowed green isosurface. Therefore, it is inferred that 2C60@C26 and 2C60@C22 may have comparable stability. Finally, in the case of 2C60@C30, the oversized ring of C30 makes it difficult to symmetrically bind two C60 fullerenes. So, only one C60 fullerene interacts with all atoms on the cyclocarbon, while the other one binds obliquely to the cyclocarbon, resulting in a relatively limited interaction. Therefore, it is reasonable to expect that 2C60@C30 is less stable than 2C60@C22 and 2C60@C26. ). It can be seen that for the complexes involving C18, C22, and C26, the binding energy of the second C60 fullerene is clearly more negative than that of the first one, that is, the presence of the first C60 fullerene significantly promotes the binding of the second one, reflecting a synergistic effect within the systems. However, if the size of the cyclocarbon is too large to bind two C60 fullerenes compactly at the same time, not only will there be no synergistic effect, but anti-synergistic effect will occur. This is the case for 2C60@C30. When the second C60 fullerene binds in 2C60@C30, the energy reduction is only half that of the first one, which results in the total binding energy of 2C60@C30 being more positive relative to that of 2C60@C26.