The LDA method which depends on homogeneous charge distribution does not regularly predict accurate chemical bonding properties, therefore, it is required to modify the LDA energy density. In the GGA scheme, electron density and each coordinate of the system are considered with the gradient of the density, therefore known as Generalised-Gradient approximations . The inclusion of higher derivatives of electron density and density gradient provides better results in comparison to the LDA method. The general form of the GGA exchange-correlation functional is given below;