“Solids Under Pressure”

N. E. CHRISTENSEN; R. E. ALONSO; D.L. NOVIKOV; A. SVANE

Grenoble, Francia

Congreso; General Conference of the Codensed Matter' division of the EPS in Grenoble; 1998

<!-- /* Font Definitions */ @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:-1610611985 1107304683 0 0 415 0;} @font-face {font-family:Times; panose-1:2 2 6 3 5 4 5 2 3 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:536881799 -2147483648 8 0 511 0;} @font-face {font-family:"WP Greek Century"; mso-font-charset:2; mso-generic-font-family:auto; mso-font-pitch:variable; mso-font-signature:0 0 0 0 0 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin:0in; margin-bottom:.0001pt; mso-pagination:widow-orphan; mso-layout-grid-align:none; punctuation-wrap:simple; text-autospace:none; font-size:10.0pt; font-family:"Times New Roman","serif"; mso-fareast-font-family:"Times New Roman";} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-size:10.0pt; mso-ansi-font-size:10.0pt; mso-bidi-font-size:10.0pt;} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.0in 1.0in 1.0in; mso-header-margin:.5in; mso-footer-margin:.5in; mso-paper-source:0;} div.Section1 {page:Section1;} --> Ab initio electronic-structure calculations are used to derive physical properties of solids. As examples we shall discuss recent structural optimizations for compound semiconductors, as well as Si under pressure. The recent ´rejection´ on the basis of experiments of the site-ordered  $-tin structure as a possible high-pressure phase of III-V compounds appears to be consistent with theoretical calculations, but stability analysis of the more ´exotic´ structures requires an accuracy that hardly can be achieved at the present. The Cmcm and Imm2 structures were optimized for several compounds in a large pressure range using the LMTO method combined with steepest-decent optimizing. For Cmcm 5 structural parameters need to be determined at each volume. Also a few metals will be considered, and in these cases emphasis is on electronic topological transitions (ETT) and their influence on elastic properties and thermal expansion coefficients. The ETTs causing the anomalies in c/a in Zn and Cd are discussed, and the phenomenon of ´pressure hardening´ of (polycrystalline) metals is illustrated by calculations on W and Mo. Most of the calculations are performed within the LDA, but corrections, such as GGA, SIC or LDA+U, may affect the predicted structural properties. The LMTO method in a full-potential implementation, including ´local orbitals´, is used to solve the one-electron equations.