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DY: Dynamik und Statistische Physik

DY 53: Phasenübergänge und kritische Phänomene

DY 53.3: Vortrag

Freitag, 27. März 1998, 11:00–11:15, H2

The α ↔ β Phase Transition in Tin: A Theoretical Study Based on Density-Functional Perturbation Theory — •P. Pavone^1,2, S. Baroni^2,3, and S. de Gironcoli³ — ¹Theoretische Physik, Universität Regensburg, D-93040 Regensburg, Germany — ²CECAM, 46 Allée d’Italie, F-69007 Lyon, France — ³INFM & SISSA, via Beirut 2-4, I-34014 Trieste, Italy.

The free energies of the α and β phases of tin are calculated in the harmonic approximation using density-functional theory and density-functional perturbation theory, within the local-density approximation. At T=0 K the free energy of the β phase lies ≈ 359 cal/mole above that of the α structure. The narrower frequency range spanned by the vibrational band in the β phase makes its entropy larger at high temperature. As a consequence, the free energies of the two phases equal each other at a temperature of 38^oC, in close agreement with the observed transition temperature T_c ≈ 13^oC.