Generalized gradient approximations (GGAâ€™s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivationâ€¦ (More)

We construct a generalized gradient approximation ~GGA! for the density nxc(r,r1u) at position r1u of the exchange-correlation hole surrounding an electron at r, or more precisely for its system andâ€¦ (More)