Möller-Plesset perturbation theory
In Helgaker (T. Helgaker, Jørgensen, and Olsen 2000), we can find the MP2 energy correction:
References
Helgaker, Trygve, Poul Jørgensen, and Jeppe Olsen. 2000. Molecular Electronic-Structure Theory. John Wiley & Sons, Ltd. - Chichester. https://doi.org/10.1002/9781119019572.