code: def _atoms(atoms_string):
      
      atoms = {}
      for split in atoms_string.split(','):
          sites = split.split('.')
          el = sites.pop(0)
          sites = list(map(int, sites))
          atoms[el] = np.array(sites) - 1
      return atoms
docs: Parse the atom string.
  
      Args:
          atoms_string (str): The atoms to plot, in the form ``"C.1.2.3,"``.
  
      Returns:
          dict: The atomic indices over which to sum the DOS. Formatted as::
  
              {Element: [atom_indices]}.
  
          Indices are zero indexed for each atomic species. If an element symbol
          is included with an empty list, then all sites for that species are
          considered.