GRADIENT EXPANSION OF THE KINETIC-ENERGY DENSITY FUNCTIONAL - LOCAL BEHAVIOR OF THE KINETIC-ENERGY DENSITY

Calculations with Hartree-Fock electron densities for the rare gas atoms He through Xe show that the gradient expansion for the kinetic energy functional, T[ρ{variant}] = T0[ρ{variant}] + T2[ρ{variant}] + T4[ρ{variant}] + ... = ∫t(ρ{variant})ρ{variant} dτ, approximates the kinetic energy by averaging over the shell structure present in the true local kinetic energy density, t(ρ{variant}), and that the accuracy of the gradient expansion improves with increasing atomic number. Components of t(ρ{variant}), t0(ρ{variant}), t2(ρ{variant}) and t4(ρ{variant}), are exhibited and discussed. The defined function t(ρ{variant}) is everywhere positive. © 1979.