▎ 摘　　要

Density functional theory (DFT) calculations were used to examine the binding strength of one and two methane molecule(s) with graphene (62 and 186 carbon atoms) and model systems of aromatic hydrocarbons (benzene, pyrene, and coronene). We explored different possibilities of binding modes of methane such as one, two, and three C-H interacting with small pi-systems. Two methane molecules were considered to bind from the same as well as opposite sides of the plane of benzene and other pi-systems including graphene models. Our results show that methane molecule prefers to bind with three C-H (center dot center dot center dot) pi interactions with all the pi-systems except benzene. The preference of tripod configuration of methane on the surface of graphene systems strongly agrees with the neutron diffraction experiment of methane on graphitized carbon black. The binding strength is almost doubled by increasing the number of methane molecules from one to two. Importantly, two methane molecules prefer to bind on the same side rather than opposite sides of the plane of graphene due to stabilizing CH (center dot center dot center dot) HC interactions between them in addition to six C-H (center dot center dot center dot) pi interactions. Interestingly, binding strength contributions from CH center dot center dot center dot HC interactions (approx. 0.4-0.5 kcal/mol) of two methane molecules on the surface are analogous to methane dimer complex free from the surface of graphene. C-H stretching frequency shifts, bond lengths, and binding distances support the presence of CH (center dot center dot center dot) HC interactions between two methane molecules. Structures of complexes, binding energies, and C-H stretching frequency shifts agree with available experimental data.