Explicit expressions for T_s[ρ] and E_x[ρ] by means of padé approximants to local-scaling transformations

Based on Padé approximants to local-scaling transformations, we advance explicit expressions for the noninteracting kinetic energy functional T_s[ρ] and the exchange energy functional E_x[ρ] appearing in the exact exchange-only density functional theory. These expressions are given as explicit analytical forms depending on the one-particle density ρ and its derivatives. Numerical calculations on first-row atoms show that the present explicit functionals give values for the noninteracting kinetic energy and for the exchange energy, of the same accuracy as those involving exact local-scaling transformations. Moreover, these values compare extremely well with those obtained by direct solution of the exchange-only Kohn-Sham equations.