The Hohenberg-Kohn theorems were found to be extremely powerful, although they do not provide a direction for the computation of ground-state density of a system. Approximately one year later, Kohn and Sham published a seminal DFT paper with simple method (known as Kohn-Sham approach) for carrying-out DFT calculations. The details of Kohn-Sham approach is given in the following section.