The HF approximations correspond to the single electron concept of the electronic structure, i.e., the distribution of N-electron can be simply defined as the sum of one-electron distribution. The HF method was developed with the assumption of a single determinant form of wave-function and negligible correlation between the electrons. Due to neglected electrons correlation, the HF method produces higher energies, large band gaps and very small band width. Therefore, HF method is found to be suitable for the small organic molecule which has small number of localized electron 59 . However, the HF method fails to describe the high electron density transition materials as it ignores the collective coulomb screening 60 . Therefore, due to the aforementioned shortcoming of HF theory, the density functional theory was developed where electron density is considered as a central parameter.