Phase-space approach to the exchange-energy functional of density-functional theory

Abstract

The phase-space distribution function corresponding to a ground-state density of a many-electron system proposed earlier [S. K. Ghosh, M. Berkowitz, and R. G. Parr, Proc. Natl. Acad. Sci. USA 81, 8028 (1984)] is employed to obtain a new approximate exchange-energy functional. This is K[ρ]=(π/2) F ${\rho }^2$(r)β(r)dr, with β(r)=1/kT(r), where T(r) is the local temperature previously defined; (3/2)kT(r) is the kinetic energy per electron at r. In Thomas-Fermi theory, β=5(3${\pi }^2$ρ${)}^{\mathrm{-}2/3}$, and this formula gives (10/9) times the classical Dirac formula. This shows why the α parameter in Xα theory is normally close to ((10/9))((2/3))=0.74. Numerical calculations on atoms are performed, giving excellent results, and the exchange hole associated with the new formula is studied in detail.