Aromatic Fragmentation Based on a Ring Overlap Scheme: An Algorithm for Large Polycyclic Aromatic Hydrocarbons Using...

We present a novel and systematic fragmentation scheme to treat polycyclic aromatic hydrocarbons (PAHs) built off the molecules-in-molecules composite method. Our algorithm generates a set of biphenyl and naphthalene subsystems overlapping by whole sextet rings, ensuring all calculations are performed on aromatic molecules. Hence, our method is called Aromatic Fragmentation Based on a Ring Overlap Scheme (AroBOROS), and the generated fragments may be combined to form a hierarchy of subsystems to reduce errors for more complex PAHs. Errors are reduced to below chemical accuracy by combining subsystems that reflect the lowest energy structures determined by Clar's rule of aromatic sextets, and this is shown on two diverse test sets of PAHs ranging from 18 to 84 carbon atoms. Additionally, evaluations are performed for larger PAHs, as well as a nanotube fragment, containing up to 132 carbon atoms, and it is shown that good results may be achieved even with fragments representing an appreciably small portion of the full system.