Jacob’s ladder

Jacob’s ladder in DFT is a metaphor for the hierarchy of exchange-correlation functionals.

It has four rungs, from lowest to highest accuracy:

-LDA: Local density approximation – simplest, uses only local electron density
-GGA: Generalized gradient approximation – adds density gradient
-Hybrids: exact exchange term
-MGGA: Meta-GGA – adds kinetic energy density

Each higher rung adds more physical ingredients and computational cost