The correction to the @CT07013@ between two electrons in orbitals \(\Psi _{i}\) and \(\Psi _{j}\) for the case when the electrons possess parallel spins. It is to be subtracted from the @CT07013@ to give the total energy of the electron–electron interaction. In the @H02747@–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 \(K_{ij}\) vanishes.