External potential and the Coulombic interactions between the electrons are included in the effective potential, the details of which have been discussed later in this chapter. The firstprinciples based DFT calculations were not generally used until 1980s, due to the lack of adequate powerful computation facilities. With the development of the advanced computer system, e.g., high-performance computing (HPC) clusters, DFT based electronic structure calculations are getting more popular. At present, DFT is a leading method in solid-state physics and quantum chemistry along with several biological systems of interest .