Within this framework, different vdW-DF methods have been proposed by varying the exchange functionals. The original vdw-DF and vdw-DF2 methods employ revPBE and rPW86 exchange functionals, respectively, and have successfully provided a better description of interactions in dimers. In this work, these methods are named revPBE and rPW86, respectively, to avoid confusion between the broader vdW-DF term. The optPBE , optB88 and optB86b 50 methods are vdw-DF methods with optimized PBE, Becke88, and Becke86 functionals respectively for determining the exchange energy contribution. These methods have been reported to behave differently in terms of predicting structural parameters, binding curves and adsorption characteristics. Since DFT-D2 and D3 methods involve only improved van der Waals interaction prediction, whereas vdW-DF methods differ in terms of the exchange functionals, the terms method and functional are used interchangeably in this study.