docs: def atoms_string_from_file(filename):
          """
          Reads atomic shells from file such as feff.inp or ATOMS file
          The lines are arranged as follows:
  
          x y z   ipot    Atom Symbol   Distance   Number
  
          with distance being the shell radius and ipot an integer identifying
          the potential used.
  
          Args:
              filename: File name containing atomic coord data.
  
          Returns:
              Atoms string.
          """
          with zopen(filename, "rt") as fobject:
              f = fobject.readlines()
              coords = 0
              atoms_str = []
  
              for line in f:
                  if coords == 0:
                      find_atoms = line.find("ATOMS")
                      if find_atoms >= 0:
                          coords = 1
                  if coords == 1 and not ("END" in line):
                      atoms_str.append(line.replace("\r", ""))
  
          return ''.join(atoms_str)