Becke, A. D. (1988). Density-functional exchange-energy approximation 
with correct asymptotic behavior. Physical review A, 38(6), 3098.

Abstract
Current gradient-corrected density-functional approximations for the 
exchange energies of atomic and molecular systems fail to reproduce 
the correct 1/r asymptotic behavior of the exchange energy density. 
Here we report a gradient-corrected exchange-energy functional with the 
proper asymptotic limit. Our functional, containing only one parameter, 
fits the exact Hartree-Fock exchange energies of a wide variety of 
atomic systems with remarkable accuracy, surpassing the performance
of previous functionals containing two parameters or more.