Toward an orbital-free density functional theory of transition metals based on an electron density decomposition

To properly apply approximate kinetic energy density functionals (KEDFs) used in orbital-free density functional theory (OF-DFT) to the highly inhomogeneous electron density in transition metals, we introduce a decomposition scheme in which the electron density is partitioned into delocalized and localized parts, which makes it possible to apply a different physically justifiable KEDF to each density. Using this decomposition scheme, we demonstrate that OF-DFT is able to quantitatively reproduce Kohn-Sham- (KS-)DFT predictions of the basic bulk properties of many phases of Ag, as well as surface energies, vacancy formation energies, and elastic moduli of face-centered-cubic Ag. However, OF-DFT Ag-Al alloy properties differ substantially from those predicted by KS-DFT using nonlocal pseudopotentials. These errors are due to remaining inaccuracies in the Ag and Al local electron-ion pseudopotentials, as well as the oversimplified model KEDF used for treating the interaction KE term between the localized and the delocalized electron densities. Future extensions to improve the treatment of transition metals are briefly outlined.