Phase transition and thermodynamic properties of beryllium from first-principles calculations

We have investigated the phase transition, electronic properties, phonon dispersion curves and thermodynamic properties of beryllium (Be) at high pressures and high temperatures using the first-principles calculations based on the density functional theory (DFT). The transition pressure of Be from hexagonal-closed-packed (hcp) structure to body-centered-cubic (bcc) structure occurs at 388 GPa. The calculated phonon dispersion curves agree with experimental results. Under compression, the phonon dispersion curves of hcp Be do not show any anomaly or instability. At low pressure the phonon dispersion curves of bcc Be display imaginary frequencies along Γ-N symmetry line. Within the quasi-harmonic Debye model, the thermal equation of state and other properties including the thermal expansion coefficient, isothermal bulk modulus and its first pressure derivative, heat capacity and entropy of hcp and bcc Be are predicted.