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In the density functional (DF) theory of Kohn and Sham, the kinetic energy ofthe ground state of a system of noninteracting electrons in a general externalfield is calculated using a set of orbitals. Orbital free methods attempt tocalculate this directly from the electron density by approximating theuniversal but unknown kinetic energy density functional. However simple localapproximations are inaccurate and it has proved very difficult to devisegenerally accurate nonlocal approximations. We focus instead on the kineticpotential, the functional derivative of the kinetic energy DF, which appears inthe Euler equation for the electron density. We argue that the kineticpotential is more local and more amenable to simple physically motivatedapproximations in many relevant cases, and describe two pathways by which thevalue of the kinetic energy can be efficiently calculated. We propose twononlocal orbital free kinetic potentials that reduce to known exact forms forboth slowly varying and rapidly varying perturbations and also reproduce exactresults for the linear response of the density of the homogeneous system tosmall perturbations. A simple and systematic approach for generating accurateand weak ab-initio local pseudopotentials which produce a smooth slowly varyingvalence component of the electron density is proposed for use in orbital freeDF calculations of molecules and solids. The use of these localpseudopotentials further minimizes the possible errors from the kineticpotentials. Our theory yields results for the total energies and ionizationenergies of atoms, and for the shell structure in the atomic radial densityprofiles that are in very good agreement with calculations using the fullKohn-Sham theory.

Orbital-Free Density Functional Theory: Kinetic Potentials and Ab-Initio Local Pseudopotentials