Jacobs Ladder

Jacobs Ladder is a strategy to find the “divine functional”, that is the exchange correlation functional that can be used to solve the Kohn-Sham equations for any solid or molecule. It involves using the methods that are known to give good results and building further on these methods. The five rungs represent five steps, from the Local Density Approximation aal the way to the full divine functional.
1) Local Density Approximation, every infinitesimal volume has its own contribution independently of other volumes.
2) GGA, the gradient of the density is incorporated into the functional.
3) meta-GGA, adding the kinetic energy density to the formulation.
4) Using an exact expression for the exchange, which exists but is computationally heavy.
5) Divine functional with both exact correlation and exact exchange.