correlation energy
The difference between the Hartree–Fock energy calculated for a system and the exact non-relativistic energy of that system. The correlation energy arises from the approximate representation of the electron-electron repulsions in the Hartree–Fock method.
PAC, 1996, 68, 2223 (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2234