Formation of a “cluster molecule” (C20)2 and its thermal stability

The possible formation of a “cluster molecule” (C20)2 from two single C20 fullerenes is studied by the tight-binding method. Several (C20)2 isomers in which C20 fullerenes are bound by strong covalent forces and retain their identity are found; actually, these C20 fullerenes play the role of atoms. The so-called open-[2 + 2] isomer has a minimum energy. Its formation path and thermal stability at T = 2000–4000 K are analyzed in detail. This isomer loses its molecular structure due to either the decomposition of one of its C20 fullerenes or the coalescence of its two C20 fullerenes into a C40 cluster. The energy barriers limiting the metastable open-[2 + 2] configuration are calculated to be U = 2−5 eV.