private static Atom[] getCarbonAlpha(Structure structure) {
    List<Atom> list = new ArrayList<>();

    for (Chain chain : structure.getChains()) {
        for (Group group : chain.getAtomGroups()) {
            try {
                Atom atom = group.getAtom("CA");
                list.add(atom);
            } catch (StructureException e) {
                System.err.println(e.getMessage());
            }
        }
    }
    return list.toArray(new Atom[list.size()]);
}