title: Density functional theory is straying from the path toward the exact functional.
abstract: The theorems at the core of density functional theory (DFT) state that the energy of a many-electron system in its ground state is fully defined by its electron density distribution. This connection is made via the exact functional for the energy, which minimizes at the exact density. For years, DFT development focused on energies, implicitly assuming that functionals producing better energies become better approximations of the exact functional. We examined the other side of the coin: the energy-minimizing electron densities for atomic species, as produced by 128 historical and modern DFT functionals. We found that these densities became closer to the exact ones, reflecting theoretical advances, until the early 2000s, when this trend was reversed by unconstrained functionals sacrificing physical rigor for the flexibility of empirical fitting.
authors.affiliation: X-ray Structural Laboratory, A. N. Nesmeyanov Institute of Organoelement Compounds RAS, 119991 Moscow, Russian Federation. medvedev.m.g@gmail.com ib@xrlab.ru.|N. D. Zelinsky Institute of Organic Chemistry RAS, 119991 Moscow, Russian Federation.|Higher Chemical College RAS, 125047 Moscow, Russian Federation.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Medvedev
authors.affiliation: X-ray Structural Laboratory, A. N. Nesmeyanov Institute of Organoelement Compounds RAS, 119991 Moscow, Russian Federation. medvedev.m.g@gmail.com ib@xrlab.ru.
authors.forename: Ivan S
authors.initials: IS
authors.lastname: Bushmarinov
authors.affiliation: Department of Physics, Temple University, Philadelphia, PA 19122, USA.
authors.forename: Jianwei
authors.initials: J
authors.lastname: Sun
authors.affiliation: Department of Physics, Temple University, Philadelphia, PA 19122, USA.|Department of Chemistry, Temple University, Philadelphia, PA 19122, USA.
authors.forename: John P
authors.initials: JP
authors.lastname: Perdew
authors.affiliation: X-ray Structural Laboratory, A. N. Nesmeyanov Institute of Organoelement Compounds RAS, 119991 Moscow, Russian Federation.
authors.forename: Konstantin A
authors.initials: KA
authors.lastname: Lyssenko