Becke 1988 nonlocal exchange potential

[Perry Mar <MAR \\at// ecs.umass.edu>]

 I am seeking the formulas for the Becke 1988 nonlocal exchange
 potential for the nonlocal exchange energy functional proposed in
 the paper
 Becke, A. D., "Density-Functional Exchange-Energy Approximation
 with Correct Asymptotic Behavior," Phys. Rev. A, 38(6), 3098-3100
 (1988).
 I have attempted to derive the nonlocal exchange potential by
 functional differentiation of the nonlocal exchange energy with
 respect to a particular spin density, and I would like to check
 my result.  If this potential has been published, I would
 appreciate any references to it.
 I intend to summarize any answers.
 Sincerely,
 Perry Mar
 Department of Chemical Engineering      E-mail:  mar \\at// ecs.umass.edu
 University of Massachusetts             Phone:  (413) 545-0770
 Amherst, MA  01003-3110, USA            Fax:    (413) 545-1647