An exact evaluation is given in the high-density limit of the first gradient coefficient which enters the exchange plus correlation energy in the Hohenberg-Kohn-Sham formalism for an inhomogeneous two-component (electron-hole) system. Numerical results are given for isotropic electron and hole bands for a range of values of the electron-hole mass and density ratios. An application is made to Ge under [111] strain and the surface energy is calculated in a simple model.

• Received 28 April 1976

DOI:https://doi.org/10.1103/PhysRevB.15.979