  We developed a method for calculating solid-state ground-state properties and
fundamental band-gaps using a generalized Kohn-Sham approach combining a local
density approximation (LDA) functional with a long-range explicit exchange
orbital functional. We found that when the range parameter is selected
according to the formula \gamma=A/(\eps_\inf - \eps_\tilde) where \eps_\inf is
the optical dielectric constant of the solid and \eps_\tilde= 0.84 and A=
0.216a0^(-1), predictions of the fundamental band-gap close to the experimental
values are obtained for a variety of solids of different types. For most solids
the range parameter \gamma is small (i.e. explicit exchange is needed only at
long distances) so the predicted values for lattice constants and bulk modulii
are similar to those based on conventional LDA calculations.
