Möller-Plesset perturbation theory

In Helgaker (T. Helgaker, Jørgensen, and Olsen 2000), we can find the MP2 energy correction: \[\begin{equation} \require{physics} E^{(2)}_\text{MP} % = - \sum_{ab} \sum_{ij} % \frac{ % (ai|bj) \qty[ 2(ia|jb) - (ib|ja) ] % }{ % \varepsilon_a + \varepsilon_b % - \varepsilon_i - \varepsilon_j % } % \thinspace , \end{equation}\] in which \(ab\) still indicate virtual spatial orbitals, and \(ij\) indicate occupied orbitals.

References

Helgaker, Trygve, Poul Jørgensen, and Jeppe Olsen. 2000. Molecular Electronic-Structure Theory. John Wiley & Sons, Ltd. - Chichester. https://doi.org/10.1002/9781119019572.