3.30 what='piezoelectric_tensor_geo'

With this option the code computes the piezoelectric tensor in a grid of geometries, the geometries specified as in what='mur_lc'. The results are written in different files in the directory elastic_constants. With a subsequent calculation that use what='mur_lc' or what='mur_lc_t' the code can read the file produced with this option and interpolate the piezoelectric tensor at the pressure (and temperature if what='mur_lc_t') dependent geometries. Usually the piezoelectric coefficient is calculated using frozen_ions=.FALSE. relaxing the atomic positions for each distorted configuration. In this case the piezoelectric tensor is computed within ZSISA. It is also possible to use the flag use_free_energy=.TRUE.. Together with the flags stypec (see the option what='scf_elastic_constants') the code can compute the internal parameters as a function of strain by minimizing the free energy at each temperature. These temperature dependent internal parameters are used to compute the temperature dependent piezoelectric tensors within the full free energy minimization (FFEM).

fl_piezo : the name of the file that contains the piezoelectric 
           tensor.
         Default : 'output_piezo.dat'
linterpolate_tau : if .TRUE. the atomic positions of each distorted 
           geometry used to calculate the piezoelectric tensor is
           used to find the internal parameters and the latter are
           derived with respect to the strain.
           This flag requires a iconstr_internal value for each strain
           type. 
           Default: .FALSE.
doberry : this flag must be .TRUE. to compute the Berry phase of each
          distorted configuration. It can be set to .FALSE. 
          when use_free_energy=.TRUE. and the code computes the phonons
          of each distorted configuration within FFEM.
          Default: .TRUE.