Quantum molecular dynamics simulations of lithium melting using Z-method

TL;DR

This study uses first-principles molecular dynamics with the Z-method to accurately simulate lithium's melting behavior under pressure, revealing a change in the melting line slope and analyzing properties near melting conditions.

Contribution

First application of the Z-method to lithium's melting curve, providing detailed insights into melting behavior and phase transition characteristics under pressure.

Findings

Melting curve agrees with experimental data up to 30 GPa

Predicted change in melting line slope at 8.2 GPa

No liquid-liquid phase transition observed

Abstract

We performed first-principles molecular dynamics calculations for lithium using the projector augmented waves method and the generalized gradient approximation as exchange-correlation energy. The melting curve of lithium was computed using the \textit{Z}-method technique for pressures up to 30 GPa, which agrees well with the experimental and two-phase simulated results. The change of the melting line slope from positive to negative was predicted by the characteristic shape inversion of the \textit{Z} curve at about 8.2 GPa. Through analyzing the static properties, we conclude that no liquid-liquid phase transition accompanies the occurrence of the melting line maximum, which is caused by the higher compressibility of the liquid phase compared to the solid phase. In addition, we systematically studied the dynamic and optical properties of lithium near melting curve at critical superheating and melting temperatures. It was suggested that spectra difference at critical superheating and melting temperature may be able to diagnose the homogeneous melting.