A simple derivation of a simple GGA is presented, in which all parameters (other than those in LSD) are fundamental constants, and only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked.Expand

A simple analytic representation of the correlation energy for a uniform electron gas, as a function of density parameter and relative spin polarization \ensuremath{\zeta}, which confirms the practical accuracy of the VWN and PZ representations and eliminates some minor problems.Expand

A way is found to visualize and understand the nonlocality of exchange and correlation, its origins, and its physical effects as well as significant interconfigurational and interterm errors remain.Expand

Numerical results for atoms, positive ions, and surfaces are close to the exact correlation energies, with major improvements over the original LM approximation for the ions and surfaces.Expand

Improvements over other simple functionals are also found in the exchange contributions to the valence-shell removal energy of an atom and to the surface energy of jellium within the infinite barrier model.Expand