def METHOD_NAME(**kwargs):
    """Returns a function that can be used to create a valid ValleOganov
    descriptor for a dataset.
    """
    def func(systems=None):
        species = set()
        for system in systems:
            species.update(system.get_atomic_numbers())
        final_kwargs = {
            "species": species,
        }
        final_kwargs.update(kwargs)
        return ValleOganov(**final_kwargs)
    return func