https://doi.org/10.1351/goldbook.ET07034

The correction to the Coulomb repulsion between two electrons in orbitals Ψ i and Ψ j for the case when the electrons possess parallel spins. It is to be subtracted from the Coulomb repulsion to give the total energy of the electron–electron interaction. In the Hartree–Fock theory the magnitude of the exchange repulsion is given by the exchange integral \[K_{ij}=\int \int \Psi _{i}^{\text{*}}\left(\mathbf{r}_{1}\right)\ \Psi _{j}^{\text{*}}\left(\mathbf{r}_{1}\right)\ \left(\frac{e^{2}}{r_{12}}\right)\ \Psi _{i}\left(\mathbf{r}_{2}\right)\ \Psi _{j}\left(\mathbf{r}_{2}\right) \ \mathrm{d}\mathbf{r}_{1} \ \mathrm{d}\mathbf{r}_{2}=\lt ij|ji \gt\] For the case of electrons with opposite spins Kij vanishes.*Source: *

PAC, 1999,*71*, 1919. 'Glossary of terms used in theoretical organic chemistry' on page 1938 (https://doi.org/10.1351/pac199971101919)

PAC, 1999,