docs: def _read_potentials(self, pot_dir):
          """import potentials from a directory
          """
          if self.assignments['potentials'] is not None:
              print('Potentials already imported. Will not overwrite!')
              return
          else:
              self.assignments['potentials'] = {}
  
          pot_files = sorted(glob(pot_dir + os.sep + 'pot*.dat'))
          for nr, filename in enumerate(pot_files):
              with open(filename, 'r') as fid:
                  pot_data = np.loadtxt(fid)
  
                  nids = self.nodeman.add_data(
                      pot_data[:, 2:4],
                  )
                  # store cids for later retrieval
                  self.assignments['potentials'][nr] = nids