Abstract:
The temperature dependences of the lifetime of polycubanes C$_{4+4n}$H$_8$ with $n$ = 2–5 up to their decomposition have been directly calculated using the molecular dynamics method. It has been shown that the activation energy of decomposition of these metastable clusters, in which the C-C bonds form an angle of 90$^\circ$ that is not characteristic of carbon systems, rapidly decreases with an increase in $n$ due to the lowering of the energy barrier that prevents the decomposition of the clusters. This has cast some doubt on the recently made suggestion that there exist nanotubes ($n\gg$ 1) with a square cross section. Nonetheless, the stability of bicubane ($n$ = 2) and tricubane ($n$ = 3) has proved to be sufficient for their existence at the liquid-nitrogen temperature.
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