Interactions between Methane and Polycyclic Aromatic Hydrocarbons: A High Accuracy Benchmark Study

Minimum energy structures and interaction energies are obtained for a series of polycyclic aromatic hydrocarbons (PAHs) interacting with a methane molecule. The PAHs include benzene, naphthalene, anthracene, phenanthrene, tetracene, pyrene, and coronene. Interaction energies are calculated using the highest level of theory and basis set available, that is, complete-basis-set extrapolated MP2 plus a conventional or explicitly correlated CCSD(T) correction in moderately sized basis sets. The results show that the singly coordinated minimum configuration observed earlier for benzene-methane is no longer the global minimum one for naphthalene and larger PAHs. Instead, triply coordinated geometries are lower in energy. The global minimum structures for methane interacting with extended systems like graphene sheets and carbon nanotubes are likely to be triply coordinated as well. A variety of novel dispersion-including DFT approaches are compared against the wave-function-based benchmark potential energy curves. The top performer, the B3LYP functional combined with the -D3 dispersion correction, is then employed to calculate interaction energies for methane interacting with hexabenzocoronene and circumcoronene in order to estimate the methane adsorption energy on graphite. The delicate balance between dispersion and exchange in PAH-methane interactions is elucidated using symmetry-adapted perturbation theory with a DFT description of monomers. The present study provides an important benchmark for the design and tuning of more approximate methods for an accurate description of hydrocarbon physisorption on carbon nanostructures.