X-ray diffraction experiments have shown that sodium exhibits a dramatic pressure-induced drop in melting temperature, which extends from 1000 K at $\sim 30\mathrm{GPa}$ to as low as room temperature at $\sim 120\mathrm{GPa}$. Despite significant theoretical effort to understand the anomalous melting, its origins are still debated. In this work, we reconstruct the sodium phase diagram by using an ab initio quality neural-network potential. Furthermore, we demonstrate that the reentrant behavior results from the screening of interionic interactions by conduction electrons, which at high pressure induces a softening in the short-range repulsion.

• Received 31 October 2011

DOI:https://doi.org/10.1103/PhysRevLett.108.115701