Reentrant melting of sodium, magnesium, and aluminum: General trend

Reentrant melting (in which a substance's melting point starts to decrease beyond a certain pressure) is believed to be an unusual phenomenon. Among the elements, it has so far only been observed in a very limited number of species, e.g., the alkali metals. Our density functional theory calculations reveal that this behavior actually extends beyond alkali metals to include magnesium, which also undergoes reentrant melting, though at the much higher pressure of ∼300 GPa. We find that the origin of reentrant melting is the faster softening of interatomic interactions in the liquid phase than in the solid, as pressure rises. We propose a simple approach to estimate pressure-volume relations and show that this characteristic softening pattern is widely observed in metallic elements. We verify this prediction in the case of aluminum by finding reentrant melting at ∼4000 GPa. These results suggest that reentrant melting may be a more universal feature than previously thought.