Structural, magnetic and electronic properties of copper-phthalocyanine (CuPc) adsorbed on graphene: Ab initio studies

Abstract

The energetics, electronic and magnetic properties of copper-phthalocyanine (CuPc) adsorbed on graphene have been studied, using the density-functional theory with variants of GGA and LDA as the exchange-correlation functionals. The effects of van der Waals (vdW) dispersion correction on the calculated properties are also investigated. Five different adsorption sites of CuPc on graphene have been considered. Our results shows that the vdW dispersion has significant effects on the final relaxed structure of the CuPc/graphene system and the CuPc adsorption process on graphene. As an illustration, we find that in the case of PBE functional, the graphene substrate remains almost flat after the CuPc adsorption whereas there is significant departure from graphene planar geometry when the vdW dispersion correction (i.e., PBE + vdW) is included. Also, with the PBE functional, the CuPc molecule adsorption process is that of physisorption whereas with the inclusion of vdW dispersion correction, the molecule is chemisorbed. However, for both the PBE functional and PBE + vdW dispersion correction, the CuPc molecule prefers to bind on the hollow site. Also, the energetically preferred CuPc adsorption site may depend on the CuPc concentration on graphene. Finally, we found that the CuPc/graphene nanocomposite acquires a magnetic moment of 1.0 μB. Our work highlights the influences of exchange-correlation functionals as well as vdW forces on the nature of interactions between an organic molecule and the graphene substrate.