  In recent work, generalized gradient approximations (GGA's) have been
constructed from the energy density of the Airy gas for exchange but not for
correlation. We report the random phase approximation (RPA) conventional
correlation energy density of the Airy gas, the simplest edge electron gas, in
which the auxiliary noninteracting electrons experience a linear potential. By
fitting the Airy-gas RPA exchange-correlation energy density and making an
accurate short-range correction to RPA, we propose a simple beyond-RPA GGA
density functional ("ARPA+") for the exchange-correlation energy. Our
functional, tested for jellium surfaces, atoms, molecules and solids, improves
mildly over the local spin density approximation for atomization energies and
lattice constants without much worsening the already-good surface
exchange-correlation energies.
