Thomas–Fermi term as the simplest correction to the Weizsacker term

The nature of the correlation function G (1,2) appearing in the definition of the reduced first order density operator γ′(1,2) = ρ(1) 1/2 ρ(2) 1/2 G (1,2) is analyzed. It is shown that when G (1,2) is expanded in terms of plane waves in the context of a single‐determinant approximation to the wave function, the correction to the Weizsacker term in the kinetic energy density expression is the Thomas–Fermi term.