Relative stability of α and β boron

摘要: α and β rhombohedral boron are closely related structures with nearly identical stability. Unlike a, in which every site is fully occupied, characterized by partial occupancy intrinsic disorder. Optimizing the occupation yields a superstructure of that we call β'. Its energy lower than but its symmetry β. The configurational entropy drives β'→ transition around room temperature. Comparing vibrational density states, find β' has an excess low frequency modes strongly localized partially occupied sites. these adds to further stabilize structure compared α.