Regensburg 2002 – wissenschaftliches Programm
HL 38.9: Poster
Donnerstag, 14. März 2002, 16:30–19:00, Poster A
Ab initio study of anharmonic properties in semiconductors: The Grüneisen tensor — •Gerd Birner, Gernot Deinzer, Pasquale Pavone, and Dieter Strauch — Institut für Theoretische Physik, Universität Regensburg, Germany
The Grüneisen tensor describes the relative change of frequencies in solids, if a macroscopic strain is applied. For homogeneous deformations of crystals with cubic symmetry, it is possible to gain the volume dependence of the frequencies on the variation of the lattice parameter . In the general case of arbitrary deformations, perturbation theory to first order in the anharmonic potential allows to express the Grüneisen tensor in terms of harmonic and anharmonic force constants . In this work, we present an ab initio study of the complete Grüneisen tensor of the tetrahedral semiconductors Si, Ge, and GaAs. Within the harmonic approximation, interatomic force constants are calculated using density-functional perturbation theory. Anharmonic coefficients of third order are derived by application of the 2n+1 theorem to the density-functional formalism. The volume mode-Grüneisen parameters obtained by our approach are very similar to those derived by the standard—quasi-harmonic—approximation. However, our method allows to extract in a direct way the off-diagonal elements of the Grüneisen tensor, which are less efficiently obtained by the standard approach.
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