The energetics of even and odd linear Cncarbon chain clusters are investigated by hybrid density functional theory (DFT) calculations. These molecular species are especially interesting due to their recent observation inside carbon nanotubes by polarized resonant Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM) by different research groups. Neutral, anionic and dianionic carbon chains were studied with sizes up to n= 75, although most presented calculations are limited to n≤ 24. Aggregation into longer chains is favored for neutral and anionic chains of any size. The barrier to aggregation of 2Cn↔ C2n is of the order of 40–20 kcal mol−1, which gradually decreases with increasing chain size, n. These barriers can be overcome during the high temperature synthesis or annealing conditions, but not when cooled down for the HRTEM and Raman experiments. Therefore, in addition to the already observed long chains also shorter chains should be observable under appropriate conditions inside carbon nanotubes.
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