ALPHA[--]BETA PHASE-TRANSITION IN TIN - A THEORETICAL-STUDY BASED ON DENSITY-FUNCTIONAL PERTURBATION-THEORY

The free energies of the alpha and beta phases of tin are calculated i n the harmonic approximation using density-functional theory and densi ty-functional perturbation theory, within the local-density approximat ion. At T=0 K the free energy of the beta phase lies approximate to 35 9 cal/mole above that of the alpha structure. The narrower frequency r ange spanned by the vibrational band in the beta phase makes its entro py larger at high temperature. As a consequence, the free energies of the two phases equal each other at a temperature of 38 degrees C, in c lose agreement with the observed transition temperature T-c approximat e to 13 degrees C. [S0163-1829(98)03714-X].