DENSITY FUNCTIONALS FROM LDA TO GGA

For ab initio calculations in quantum chemistry, materials science, bi ochemistry, and nanoelectronics, the Kohn-Sham density functional theo ry is a widely used method to solve the ground-state many-electron pro blem. Density functional theory requires approximations for the exchan ge-correlation (xc) energy as a functional of the density. The simples t approximations are the local density approximation (LDA) and the loc al spin density (LSD) approximation, which employ the re energy of the (respectively, spin-unpolarized and spin-polarized) uniform electron gas as an input. Generalized gradient approximations (GGA's) go beyond the LDA and LSD descriptions by including density gradients, and impr ove calculated results significantly. Some GGA success stories are sum marized. (C) 1998 Elsevier Science B.V.