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., Nature 2023 , 623, 972] of the cyclic C 10 reveal a cumulenic pentagon-like D 5h structure at ∼5 K. However, the long-standing presumption that a large zero-point vibrational energy combined with an extremely flat D 5h ↔ D 10h ↔ D 5h isomerization pathway washes out the pentagonal D 5h structure and yields a symmetric D 10h 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 5h -D 10h potential energy barrier (benchmarked previously by others). Large scale diffusion Monte Carlo simulations in full dimensionality show that the vibrational ground state of C 10 has compositional character of more than 96% D 5h , fully reflecting the experimental imaging data. Quantum mechanical variational calculations in 1-D further suggest persistence of the D 5h symmetry structure at higher temperatures.