ИСТИНА

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 (1). For years, DFT development focused on energies, implicitly assuming that functionals producing better energies become better approximations of the exact functional. We have examined the other side of the coin — the energy-minimizing electron densities for atomic species, as produced by more than a hundred DFT functionals (2). Self-consistent electron densities produced by these functionals were compared to the CCSD-full ones by means of three local descriptors: electron density (RHO), its gradient norm (GRD) and its Laplacian (LR); aug-cc-pωCV5Z basis set was used for all calculations. We have found that, reflecting theoretical advances, DFT functionals’ densities became closer to the CCSD-full ones, until in the early 2000s this trend was reversed by flexible functionals with forms chosen to be suitable for empirical fitting. During the years 2017 and 2018 this result was extensively discussed in scientific literature and significantly broadened (3–11).