Role of quantum ion dynamics in the melting of lithium

The role of quantum ion dynamics in the low melting temperatures of Li is investigated from first principles theory. Free energies of solid and liquid phases are obtained at the classical and quantum ion levels. The results are used to determine the Li melting curve in the 40-60 and 110-150 GPa pressure ranges and are in excellent agreement with experimental data around 50 GPa. They predict the resumption of a positive melting slope at higher pressure. Quantum corrections to individual energy terms are far more significant than their net effect on the melting temperatures near 50 GPa, even though lithium behaves as a quantum solid at this pressure. The scales of these corrections increase with compression. A case is made for the possibility for anomalous melting at much higher pressures, where quantum ion dynamics are expected to play a prominent role.