import itertools


def _tag_list(elements):
    """
    Internal helper function that returns a list of tags
    from a list of elements

    Args:
        elements (list[str]): list of elements .f.e ["Si", "C"]

    Returns:
        list[str]: list of tags f.e. ["SiSiSi", "SiSiC", ...]
    """
    return ["".join(el) for el in itertools.product(elements, repeat=3)]