  In this paper, we investigate the adsorption of water monomer on fluorinated
graphene using state-of-the-art first principles methods within the framework
of density functional theory (DFT). Four different methods are employed to
describe the interactions between water and the carbon surface: The traditional
DFT calculations within the generalized gradient approximation (GGA), and three
types of calculations using respectively the semi-empirical DFT-D2method, the
original van der Waals density functional (vdW-DF) method, and one of its
variants. Compared with the adsorption on pristine graphene, the adsorption
energies of water on fluorinated graphene are significantly increased, and the
orientations of water diploe moment are notably changed. The most stable
configuration is found to stay right above the top site of the C atom which is
bonded with F, and the dipole moment of water molecule aligns spontaneously
along the surface normal.
