Quantum Monte Carlo Simulations of the Vibrational Wavefunction of the Aromatic Cyclo[10]carbon Using a Full Dimensional Permutationally Invariant Potential Energy Surface.

New experimental measurements [Sun et al., , 623, 972] of the cyclic C reveal a cumulenic pentagon-like D structure at ∼5 K. However, the long-standing presumption that a large zero-point vibrational energy combined with an extremely flat D ↔ D ↔ D isomerization pathway washes out the pentagonal D structure and yields a symmetric D decagon remains at odds with the experiment. We resolve this issue with our fitting approach based on a bond-order charge-density matrix expressed in permutationally invariant polynomials. We train the model on τHCTH/cc-pVQZ data morphed to reproduce a relativistic all-electron CCSDT(Q)/CBS D-D potential energy barrier (benchmarked previously by others). Large scale diffusion Monte Carlo simulations in full dimensionality show that the vibrational ground state of C has compositional character of more than 96% D, fully reflecting the experimental imaging data. Quantum mechanical variational calculations in 1-D further suggest persistence of the D symmetry structure at higher temperatures.