Möller-Plesset perturbation theory

In Helgaker (T. Helgaker, Jørgensen, and Olsen 2000), we can find the MP2 energy correction: E(2)MP=abij(ai|bj)[2(ia|jb)(ib|ja)]εa+εbεiεj, 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.