The potential energy component corresponding to the electrostatic interaction between each pair of charged particles: \[V=\frac{1}{4\: \pi\: \varepsilon_{0}}\ \sum _{i}\sum _{j \lt i}e_{i}\ e_{j}\ \Delta r_{ij}\] where \(\varepsilon _{0}\) is the @P04507@ of a vacuum, \(\Delta r_{ij}\) is the distance between the two particles, and \(e_{i}\) and \(e_{j}\) are the charges on particles \(i\) and \(j\). In @M03996@ theory, the electrostatic repulsion between the two electrons occupying the orbitals \(\Psi _{i}\) and \(\Psi _{j}\). In the @H02747@–Fock method, the mean @C01365@ repulsion is determined by the value of the @C01366@ \[J_{ij}=\int \int \Psi _{i\text{*}}\left(\mathbf{r}_{1}\right)\ \Psi _{i}\left(\mathbf{r}_{1}\right)\ \left(\frac{e^{2}}{r_{12}}\right)\ \Psi _{j\text{*}}\left(\mathbf{r}_{2}\right)\ \Psi _{j}\left(\mathbf{r}_{2}\right) \ \mathrm{d}\mathbf{r}_{1} \ \mathrm{d}\mathbf{r}_{2} = \lt ij|ij \gt\]