Melting curve of tantalum from first principles

We report on the first-principles calculation of the melting curve of Ta in the pressure range 0-300 GPa. The calculations have been performed using density functional theory (DFT) with generalized gradient corrections and the projector augmented wave method. The melting curve has been evaluated using the method of the coexistence of phases, with the help of an auxiliary reference potential. The melting curve obtained with the reference potential has then been corrected using free energy differences between the DFT and the reference potential, so as to obtain the DFT melting curve. The results are in good agreement with diamond anvil cell experiments at low pressure, but they rapidly diverge from these as pressure is increased, and agree well with shock-wave experiments at high pressure. A general description of the lattice dynamics and thermal properties of body-centered cubic tantalum using DFT is also presented. The equation of state at zero temperature and the phonon dispersion are investigated using both the local density approximation and the generalized gradient approximation (GGA). Good agreement with the zero-temperature equation of state and zero-pressure phonon dispersions is obtained with the GGA. This agreement reinforces the reliability of the calculated melting curve.