Regensburg 2002 – wissenschaftliches Programm
HL 38.8: Poster
Donnerstag, 14. März 2002, 16:30–19:00, Poster A
Ab initio study of harmonic and anharmonic cumulants of elemental semiconductors — •Gerd Birner, Gernot Deinzer, and Dieter Strauch — Institut für Theoretische Physik, Universität Regensburg, Germany
The cumulant analysis of extended x-ray absorption fine structure (EXAFS) is regarded as the most general and practical technique to determine the local atomic configuration of materials ranging from crystalline and noncrystalline solids to liquids. In this work, we present an ab initio study of the radial and perpendicular harmonic component of the average relative thermal displacement of absorber and backscatterer atoms in crystalline Ge and Si. Furthermore, we calculated from first principles the temperature-dependent third-order anharmonic cumulants using quantum-statistical methods . This approach allows to express the cumulants in terms of harmonic and anharmonic interatomic force constants of the considered materials. Within the harmonic approximation, we evaluated force constants by Fourier deconvolution of dynamical matrices obtained using the density-functional perturbation theory. Anharmonic coefficients up to the third order are derived by the application of the 2n+1 theorem to the density-functional formalism. Our results are in good agreement with the available experimental EXAFS data for Ge .
 T. Fujikawa and T. Miyanaga, J. Phys. Soc. Jpn. 62, 4108 (1993).
 G. Dalba, P. Fornasini, R. Grisenti, and J. Purans, Phys. Rev. B 82, 4240 (1999).