Dresden 2006 – scientific programme

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DY: Dynamik und Statistische Physik

DY 50: Lattice Dynamics and Non-Linear Excitations

DY 50.2: Talk

Friday, March 31, 2006, 10:30–10:45, H\"UL 186

Phonons at the β-tin→Imma→sh phase transitions in Si: An ab-initio study — •Katalin Gaal-Nagy — Dipartimento di Fisica, Universita degli Studi di Milano, Via Celoria 16, 20133 Milano (Italy)

We present an ab-initio study of the lattice statics and dynamics of Si near the β-tin→Imma→ sh phase transitions. Our results allow a new interpretation of measured Raman phonon frequencies of what was thought to be the β-tin phase. A comparison of our data with the experimental ones shows that the phase transitions β-tin→Imma→sh have been already indicated in the Raman spectra even though not realized because of marginal changes. Furthermore, we find a soft-mode behavior for the phase transition sh→Imma. The transition pressure for the β-tin→Imma phase transition can be determined precisely from the phonon frequencies rather than from the lattice parameters. This work has been performed using the plane-wave pseudopotential approach to the density-functional theory and the density-functional perturbation theory within the local density approximation.