First-Principles Path Integral Monte Carlo Studies of the Pseudo Jahn–Teller Effect in the Aromatic Cyclo[10]carbon

There has been renewed interest in carbon nanoscale structures. Experimental measurements at 4.7 K and subsequent first-principles-based vibrational diffusion Monte Carlo simulations at 0 K recently showed that the aromatic cyclo[10]carbon prefers a <i>D</i>_5<i>h</i> pentagon-like structure to a regular <i>D</i>_10<i>h</i> decagon. This symmetry breaking is due to the second-order Jahn-Teller effect (JTE) and has been amply described in the literature for the cumulenic cyclo[4<i>m</i> + 2]carbon clusters. Yet temperature dependence of the JTE in cyclo[4<i>m</i> + 2]carbon clusters in general and the cyclo[10]carbon in particular has not been studied systematically. In this work, we employ path integral Monte Carlo simulations on a first-principles-derived permutationally invariant potential energy surface (PES) to examine the JTE in cyclo[10]carbon as a function of temperature. The PES was trained on a set of τHCTH/cc-pVQZ energies sampled up to ∼7.7 eV above the <i>D</i>_5<i>h</i> global minimum and locally adjusted to a high-level benchmark (reported by others) of the 812 cm^-1 electronic energy difference between the <i>D</i>_5<i>h</i> global minimum and the <i>D</i>_10<i>h</i> transition state. The calculations show a strong JTE at lower temperatures with a dominant <i>D</i>_5<i>h</i> composition at 100 K and a gradually diminishing JTE at higher temperatures with a washed-out pentagonal structure above 300 K.