title: Relevance of the slowly varying electron gas to atoms, molecules, and solids.
abstract: We present a Thomas-Fermi-inspired density scaling under which electron densities of atomic, molecular, or condensed matter become both large and slowly varying, so that semiclassical approximations and second-order density gradient expansions are asymptotically exact for the kinetic and exchange energies. Thus, even for atoms and molecules, density-functional approximations should recover the universal second-order gradient expansions in this limit. We also explain why common generalized gradient approximations for exchange do not.
authors.affiliation: Department of Physics and Quantum Theory Group, Tulane University, New Orleans, Louisiana 70118, USA.
authors.forename: John P
authors.initials: JP
authors.lastname: Perdew
authors.forename: Lucian A
authors.initials: LA
authors.lastname: Constantin
authors.forename: Espen
authors.initials: E
authors.lastname: Sagvolden
authors.forename: Kieron
authors.initials: K
authors.lastname: Burke