Electronic structure of materials under pressure

Parameter-free calculations based on the density-functional theory are used Co ex-amine high-pressure phases of solids. For the elemental semiconducto rs, as represented by Si, the high-pressure phases are examined in some det ail, and particular attention is paid to the Si(VI)orthorhombic (Cmca) stru cture which was resolved only very recently. For III-V semiconductors the o ptimization of the structural parameters of the Cmcm and Imm2 phases is des cribed. The structural energy differences are in several cases very small, and in some cases too small to allow a safe structure prediction on the bas is of the calculations. in that context we also discuss ways to go beyond t he local density approximation (LDA). We show that the predicted high-press ure phases may be significantly affected by inclusion of (generalized) grad ient corrections (GGA). Elemental Zn (hcp) is further taken as an example w here we find that the simple LDA leads to poor results for the equilibrium volume and axial ratio (c/a). introducing corrections, for example by GGA, it is, however, possible to achieve an accuracy that allows a study of the structural changes of Zn land Cd) under pressure and analysis of these chan ges in terms of electronic topological transitions. (C) 2000 John Wiley & S ons, Inc.