Pushing the Boundaries of Spectroscopic Accuracy: from Small Sheet to Large Bowl Models of Graphene

Polycyclic aromatic hydrocarbons (PAHs) play a pivotal role in combustion chemistry, astrochemistry, and materials science, while also serving as molecular prototypes of graphene. Rotational spectroscopy offers unparalleled structural accuracy but requires a permanent dipole moment, which arises only under specific structural distortions. To explore these conditions, we investigated PAHs where nonzero dipoles stem from ring-size mismatches, symmetry breaking, or curvature-induced polarization. Benchmark wave function methods were employed to provide reference geometries for the smaller PAHs, whereas bond-corrected double-hybrid density functionals extend spectroscopic accuracy to larger, curved systems at a reduced computational cost. The computed rotational constants reproduce the experimental values within 0.1% for all planar and curved PAHs, except for phenanthrene, whose case calls for experimental reassessment. The proposed protocol effectively bridges computation and experiment, enabling spectroscopic-level accuracy for a broad range of graphene fragments relevant to astrochemical and nanomaterials research.