The alkali metals continue to attract attention due to their enigmatic melting behavior at high pressure. In this study, ab initio molecular dynamics (AIMD) calculations for Na using the projector augmented waves method and the generalized gradient approximation as exchange-correlation energy were performed. The melting temperature $\left(T_m\right)$ results from the AIMD at extreme conditions confirm the recent findings of a $T_m$ maximum and show a decrease of $\sim 200\mathrm{K}$ between 45 and $120\mathrm{GPa}$. Furthermore, from elastic constant calculations using the exact muffin-tin orbitals method, a Lindemann model curve was calculated. The model reproduces the trend of the experimental results of Gregoryanz et al. [Phys. Rev. Lett. 94, 185502 (2005)] who reported an extraordinarily big melting temperature drop of $\sim 700\mathrm{K}$ between 31 and $118\mathrm{GPa}$.

• Received 18 June 2007

DOI:https://doi.org/10.1103/PhysRevB.77.132101