Abstract
Becke [J. Chem. Phys. 84, 4524 (1986); Phys. Rev. A 38, 3098 (1988)] has shown that the Hartree-Fock exchange energy for atoms (and molecules) can be excellently represented by a formula K=F (r)[1+βG()]dr, where is the Dirac constant, β is a constant, G(x) is a function of the gradient-measuring variable =‖∇‖/, and the summation is over spin densities . Becke recommends G()=/[1+0.0253()]. It is demonstrated that the kinetic energy can be represented with comparable accuracy by the formula T=F (r)[1+αG()]dr, where is the Thomas-Fermi constant, α is a constant, and G(x) is just the same function that appears in the formula for K. Recommended values, obtained by fitting data on rare-gas atoms, are α=4.4188×, β=4.5135×. The best α-to-β ratio, 0.979, is close to unity, and calculations with α=β=4.3952× are shown to give remarkably accurate values for both T and K. It is briefly discussed how the above-noted equations for K and T can both result from scaling arguments and a simple assumption about the first-order density matrix.
- Received 11 March 1991
DOI:https://doi.org/10.1103/PhysRevA.44.768
©1991 American Physical Society