private static List<Atom> getPhosphorus(Chain chain) {
    List<Atom> list = new ArrayList<>();

    for (Group group : chain.getAtomGroups()) {
        try {
            Atom atom = group.getAtom("P");
            list.add(atom);
        } catch (StructureException e) {
            System.err.println(e.getMessage());
        }
    }
    return list;
}