Exchange-correlation energy functional gradient-corrected

In practice, only approximate expressions are known for the exchange-correlation density functional xcM and the most important ones stem from two classes the generalized gradient approximation (GGA) functionals also called gradient-corrected functionals and their combination with the exact exchange energy expression 52 =i / known from Hartree-Fock theory denoted hy-... 

Approximate gradient-corrected exchange and correlation energy functionals are developed using theoretical considerations such as the known behavior of the true (but unknown) functionals and E in various limiting situations as a guide, with, per-... 

Non-Local Density Approximation A density functional theory (DFT) method with the exchange-correlation energy correction containing the electron density gradient. 

---