Lattice dynamics and thermodynamic properties of the beta-Sn phase in Si

The lattice dynamics of silicon in the metastable beta -Sn structure is stu died using the density-functional linear-response theory. The Gruneisen par ameters and thermal expansion are calculated in the quasiharmonic approxima tion for the cubic diamond led) and beta -Sn phase and the thermodynamic pr operties are compared with the liquid phase at zero pressure. We relate the anomalously high entropy of fusion in Si to the difference in entropy betw een the beta -Sn and the ed phase. The melting temperature and phase bounda ry slopes for the beta -sn phase at zero pressure are qualitatively differe nt from those deduced from the experimental pressure-temperature phase diag ram. This suggests that the reported experimental liquid-metallic solid pha se boundary does not refer to the beta -Sn phase.