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.