  In this paper, an exchange functional which is compatible with the non-local
Rutgers-Chalmers correlation functional (vdW-DF) is presented. This functional,
when employed with vdW-DF, demonstrates remarkable improvements on
intermolecular separation distances while further improving the accuracy of
vdW-DF interaction energies. The key to the success of this three parameter
functional is its reduction of short range exchange repulsion through matching
to the gradient exchange approximation in the slowly varying/high density limit
while recovering the large reduced gradient, s, limit set in the revised PBE
exchange functional. This augmented exchange functional could be a solution to
long-standing issues of vdW-DF lending to further applicability of density
functional theory to the study of relatively large, dispersion bound (van der
Waals) complexes.
