Improving the understanding of the melting curve of tantalum at extreme pressures through the pressure dependence of fusion volume and entropy

Molecular dynamics simulations of the melting curve of tantalum for the pressure range 0–300 GPa are reported. The calculated melting curve agrees well with shock wave measurements and other calculations, but disagrees strongly with the diamond anvil cell data at high pressure. Calculated results for the pressure dependence of the fusion volume and entropy show that the pressure dependence of melting temperature approximately followed the Clausius–Clapeyron relation, and the slope of melting curve is mainly due to the variation of fusion volume. Entropy change due to latent volume change in melting, ΔS_V$\mathrm{\Delta }{S}_V$ and change in the configuration, ΔS_D$\mathrm{\Delta }{S}_D$ were evaluated. It is found that they have similar trend as the overall entropy change in melting, and ΔS_D$\mathrm{\Delta }{S}_D$ is more dominant. Furthermore, the value of ΔS_D$\mathrm{\Delta }{S}_D$ at ambient pressure is close to Rln  2 per mole, which is the specific value of ΔS_D$\mathrm{\Delta }{S}_D$ predicted by the Rln2 rule, while it decreases when pressure goes from 50 to 300 GPa. The analysis of the pair distribution function at extreme pressure shows that the change of configuration on melting decreases with increasing pressure, which supports the pressure dependence of ΔS_D$\mathrm{\Delta }{S}_D$.