1.25 How do I calculate the temperature dependent elastic constants of a solid relaxing the internal degree of freedom?

This is possible only within the ZSISA approximation. This means that for each value of the crystal parameters the ions are relaxed (with frozen_ions=.FALSE.) to their T = 0 K equilibrium positions. The phonons (and the free energy) are computed only in this configuration. For solids in which internal relaxations are described by one degree of freedom, it is possible to compute the phonons (and the free energy) for several values of this parameter. The free energy as a function of this parameter is then minimized at each strain and each temperature (See the parameter stype in what='scf_elastic_constants').