code: def total_surface_energy(self):
          
          tot_surface_energy = 0
          for hkl in self.miller_energy_dict.keys():
              tot_surface_energy += self.miller_energy_dict[hkl] * \
                                    self.miller_area_dict[hkl]
          return tot_surface_energy
docs: Total surface energy of the Wulff shape.
  
          Returns:
              (float) sum(surface_energy_hkl * area_hkl)