We present a general theory of compounds with partial long-range order. We derive a simple formula that determines the properties of a partially ordered compound from those of the perfectly random alloy and the fully ordered compound. The formula makes accurate predictions of both formulation energies and electronic band structures. We also use the formula to predict the band gaps of ${\mathrm{Al}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ga}}_{\mathit{x}}$As/GaAs superlattices.

• Received 10 September 1992

DOI:https://doi.org/10.1103/PhysRevLett.69.3766