The selected DFT methods in this work are PBE , PBE-D2 , PBE-D3 , RPBE , RPBE-D2 , RPBE-D3 , vdW-DF , vdW-DF2 , optPBE, optB88 and optB86b which are implemented in Vienna Ab-initio simulation package (VASP). The functionals PBE and RPBE are considered as dispersion-excluded reference functionals on account of their vast application in computational heterogeneous catalysis. So far, a large number of theoretical studies with generalized gradient approximation (GGA) has been based on Grimmie's semi-empirical DFT-D dispersion correction methods. DFT-D methods hinge upon incorporating a semi-empirical correction to the energy obtained from DFT calculation to account for the dispersion interactions. In the DFT-D2 method, the dispersion included total energy is given by