Phonon instability and structural phase transition in Vanadium under high pressure

Results of the first-principles calculations are presented for the group-VB metals V, Nb and Ta up to couple of megabar pressure. An unique structural phase transition sequence BCC–>(at 60 GPa) rhombohedral (angle=110.5 degree)–>(at ~ 160 GPa)rhombohedral(angle=108.5 degree)–> (at ~ 430 GPa) BCC is predicted in V. We also find that BCC-V becomes mechanically and vibrationally unstable at around 112 GPa pressure. Similar transitions are absent in Nb and Ta.