I want to calculate Gibbs free energy for the solid phase of the silicon and the liquid phase of the silicon. As far as I can see there are ways how to calculate Enthalpy and temperature but there are no ways to calculate entropies. I need entropy because G = H - T*S. I want to plot those two energies as function of temperature and from that to try to determine the melting temperature.
Calculating free energies is a non-trivial topic. There
is no simple formula that LAMMPS (or any other code)
can use to do this.
PLUMED can do that.