              The value of _chem_comp_atom.atom_id must uniquely identify\
               each atom in each monomer in the CHEM_COMP_ATOM list.\
\
               The atom identifiers need not be unique over all atoms in the\
               data block; they need only be unique for each atom in a\
               component.\
\
               Note that this item need not be a number; it can be any unique\
               identifier.