The phase diagram of tungsten at high pressure predicted by first principles calculations

By using the particle swarm optimization algorithm, low-energy structures of tungsten are searched under pressure. The results show the double hexagonal close-packed (dhcp) structure is the most stable phase at high pressures. The phase transition pressure from the body-centered cubic (bcc) structure to the dhcp structure is 1115 GPa. By employing the self-consistent ab initio lattice dynamics method to take anharmonic effects into account, phonon dispersion curves of the dhcp phase are derived at various temperatures and pressures. The results demonstrate the dynamical stability of the dhcp phase in a wide pressure–temperature region. By analyzing the Gibbs free energy, the bcc–dhcp phase boundary in the 300–8000 K range is established and lies above 1041 GPa.