code: def get_frequency_shift(
              self,
              grid_points,
              temperatures=np.arange(0, 1001, 10, dtype='double'),
              epsilons=None,
              output_filename=None):
          
  
          if self._interaction is None:
              self.set_phph_interaction()
          if epsilons is None:
              _epsilons = [0.1]
          else:
              _epsilons = epsilons
          self._grid_points = grid_points
          get_frequency_shift(self._interaction,
                              self._grid_points,
                              self._band_indices,
                              _epsilons,
                              temperatures,
                              output_filename=output_filename,
                              log_level=self._log_level)
docs: Frequency shift from lowest order diagram is calculated.
  
          Args:
              epslins(list of float):
                 The value to avoid divergence. When multiple values are given
                 frequency shifts for those values are returned.