Görling–Levy pertubation theory

Görling–Levy perturbation theory (GLPT) in Kohn–Sham (KS) density functional theory (DFT) is the analogue to what Møller–Plesset perturbation theory (MPPT) is in Hartree–Fock (HF) theory. Its basis is Rayleigh–Schrödinger perturbation theory (RSPT) and the adiabatic connection (AC). It describes electronic correlation effects. It is mostly used to second (GL2), rarely to third (GL3) or fourth (GL4) order, but becomes fast really increasingly computational expensive. It was published in 1993 and 1994 by Andreas Görling and Mel Levy.