Density functional theory exchange-correlation energy

The pairwise interaction may be obtained using density functional theory. Let pA and pB be the density for individual A and B subsystems. In terms of density functional theory, the interaction energy EAB consists of correlation, kinetic energy, and exchange and electrostatic contributions, or... 

Gritsenko, O. V., Schipper, P. R. T., Baerends, E. J., 1997, Exchange and Correlation Energy in Density Functional Theory. Comparison of Accurate DFT Quantities With Traditional Hartree-Fock Based Ones and Generalized Gradient Approximations for the Molecules Li2, N2, F2 , J. Chem. Phys., 107, 5007. 

Wesolowski, T. A., Parisel, O., Ellinger, Y., Weber, J., 1997, Comparative Study of Benzene---X (X = 02, N2, CO) Complexes Using Density Functional Theory The Importance of an Accurate Exchange-Correlation Energy Density at High Reduced Density Gradients , J. Phys. Chem. A, 101, 7818. 

The density functional theory (DFT) [32] represents the major alternative to methods based on the Hartree-Fock formalism. In DFT, the focus is not in the wavefunction, but in the electron density. The total energy of an n-electron system can in all generality be expressed as a summation of four terms (equation 4). The first three terms, making reference to the noninteracting kinetic energy, the electron-nucleus Coulomb attraction and the electron-electron Coulomb repulsion, can be computed in a straightforward way. The practical problem of this method is the calculation of the fourth term Exc, the exchange-correlation term, for which the exact expression is not known. 

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