16 How do I calculate the equilibrium structure?

Use what='mur_lc'. See example05. Refer to the user's guide for anisotropic solids. The crystal parameters are written in the thermo_pw output file. Note that the structure is searched interpolating with a polynomial or with the Murnaghan equation the energy calculated for several geometries close to the geometry given in the input of pw.x so the closer this structure is to the actual equilibrium structure the better the fit is and the closer the value found by thermo_pw to the real minimum. If the equilibrium structure is very different from the one given in the pw.x input you might want to repeat the calculation starting from the new equilibrium structure. You can also check with the file output_mur.ps (when lmur=.true.) or output_energy.ps (when lmur=.false.) if the minimum found is within the range of calculated structures. If this is not the case the minimum has probably a non negligible error. Note also that almost all options can be specified using what='mur_lc_...' instead of what='scf_...'. In this case they are calculated at the equilibrium geometry instead of the geometry given in the pw.x input. This holds also if a finite pressure is specified in the thermo_pw input and the equilibrium structure corresponds to the given pressure (See below).