PAF64 database
We construct a comprehensive database of CCSD(T) isomerization energies of 64 perfluorinated polycyclic aromatic hydrocarbons (PAFs) and corresponding polycyclic aromatic hydrocarbons (PAHs) using the G4(MP2) composite ab initio method. The considered PAF and PAH compounds are (number of isomers given in parentheses): C12X8 (2), C14X10 (2), C16X10 (2), C17X12 (11), C18X12 (5), C19X12 (12), C20X12 (21), C21X14 (3), and C22X12 (6) (X = H, F). This database includes a diverse range of structural motifs, including planar and non-planar configurations, and exhibits unique stability trends influenced by steric effects and F•••F repulsion. Perfluorination significantly alters the relative stabilities of the PAH isomers, with some isomer sets exhibiting complete reversals in energetic ordering. We use the G4(MP2) benchmark isomerization energies to evaluate the performance of 35 DFT and 12 dispersion-corrected DFT-D4 methods. We show that the PAF isomerization energies pose a substantial challenge for DFT methods. D4 dispersion corrections are critical for attaining mean absolute deviations (MADs) below the threshold of chemical accuracy (i.e., below 4.2 kJ mol–1). The best-performing methods from each rung of Jacob’s Ladder are (MADs given in parentheses): BLYP-D4 (4.5), M06-L-D4 (4.8), B3PW91-D4 (3.4), and PW6B95-D4 (3.3 kJ mol–1). Overall, B3PW91-D4 emerges as the best functional, achieving high accuracy while also successfully predicting the most stable isomers in challenging cases. This study underscores the current limitations of many DFT methods and provides critical guidance for future studies on electron-deficient aromatic systems, including perfluorinated nanomaterials such as graphene derivatives, fullerenes, and carbon nanotubes.
