  We present here a formulation for the calculation of the
configuration-averaged optical conductivity in random alloys. Our formulation
is based on the augmented-space theorem introduced by one of us [A. Mookerjee,
J. Phys. C: Solid State Phys. 6, 1340 (1973)]. We show that disorder scattering
renormalizes the electron and hole propagators as well as the transition
amplitude. The corrections to the transition amplitude have been shown to be
related to the self-energy of the propagators and vertex corrections.
