A generalized version of Hartree and Hartree-Fock theory is the now famous Kohn-Sham (KS) theory. Kohn-Sham theory is so popular that it is often used as synonymous to DFT (this is not the case, as there is interesting research on Orbital-Free versions). Unlike the earlier, Thomas-Fermi theory, which approximates the kinetic-energy by a density-functional, KS theory instead approximates electronelectron interactions by a density-functional and treats the kinetic-energy exactly, within this theory. Following Hartree, and Hartree-Fock's theory, the novel feature is the inclusion of the (α|β) σ XC operator which would compute the effective electron-electron interaction, via a density-functional including exchange and correlation. Like, HF theory, this operator is diagonalized and reconstructed until convergence is reached. For a more detailed discussion the reader is referred to (chapter 2, reviews static KS-DFT).