Intermolecular interaction in density functional theory: Application to carbon nanotubes and fullerenes

A theoretical study of weak interactions in graphitic materials such as carbon nanotubes (CNTs), fullerenes, and graphene is presented here. Based on a localized orbital density-functional theory formalism, our treatment which has already been applied for graphene-graphene interaction describes independently the weak chemical as well as the van der Waals interactions with high accuracy. The weak chemical interaction is described in the frame of the linear combination of atomic orbital S² model based on a weak overlap expansion, and the van der Waals interaction is treated in the dipolar approximation, taking into account virtual transitions of high energy. This formalism is applied here to the case of lateral interaction between CNTs, C₆₀ dimers, adsorption of C₆₀ on graphene and CNT, and encapsulation of C₆₀ and CNT. The power law of the interaction is analyzed, and useful parameters such as C₆ coefficients and an exponential model for the ``chemical'' interaction are extracted. Beyond the study of graphitic materials, this work opens interesting perspectives in the analysis of weakly bonded metal/organics interfaces.