  Recent reports of the melting curve of sodium at high pressure have shown
that it has a very steep descent after a maximum of around 1000K at 31 GPa.
This is not due to a phase transition. According to the Lindemann criterion,
this behaviour should be apparent in the evolution of the Debye temperature
with pressure. In this work, we have performed an "ab-initio" analysis of the
behaviour of both the Debye temperature and the elastic constants up to 102
GPa, and find a clear trend at high pressure that should cause a noticeable
effect on the melting curve.
