  The high pressure lattice dynamics of rhombohedral antimony have been studied
by a combination of diffuse scattering and inelastic x-ray scattering. The
evolution of the phonon behavior as function of pressure was analyzed by means
of two theoretical approaches: density functional perturbation theory and
symmetry-based phenomenological phase transition analysis. This paper focuses
on the first structural phase transition, SbI-SbIV, and the role of vibrations
in leading the transition. The phonon dispersion exhibits complex behaviour as
one approaches the structural transition, with the branches, corresponding to
the two transitions happening at high pressure in the Va elements (A7-to-BCC
and A7-to-PC) both showing softening.
