Exact Exchange in Orbital-Free Density-Functional Theory

Ivan P. Bosko and Viktor N. Staroverov

Department of Chemistry, The University of Western Ontario, London, Ontario N6A 5B7, Canada

We show that the Fermi–Amaldi functional is the exact exchange functional within the orbital-free Levy–Perdew–Sahni (LPS) equation for the square root of the electron density. This result follows from a reinterpretation of the LPS scheme based on a reference system of non-interacting boson-like fermions occupying a single spatial orbital. In contrast to the orbital-dependent Kohn–Sham exact exchange, the exact LPS exchange is explicitly multiplicative and fully compatible with the orbital-free formalism. Self-consistent calculations for atoms and molecules demonstrate improved accuracy relative to conventional LPS approximations. These findings provide a foundation for incorporating exact exchange and hybrid-functional concepts into the orbital-free LPS framework.

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