Semiempirical MO Methods, Deduced from Density Functional Theory

An effort is made to introduce LCAO into density functional theory. The exchange-correlation energy expression given by Gunnarsson and Lundqvist gives then the correlation energy as a sum of pair-correlation energies to leading order. Following Sinanoglu these are added to the repulsion integrals, and the total energy expression of semiempirical theories is thus obtained. The orbitals of semiempirical theories are obtained as "Kohn-Sham orbitals" in density functional theory. It is finally observed that Koopmans' theorem should not be used to obtain ionization energies when the correlation has been taken care of.