def _element_list(an, no):
    """Binary mapping of homoatomic interactions.

    Parameters
    ----------
    an : list
        List of atom numbers.
    no : int
        Select atom number.
    """
    binary_inter = []
    for n in an:
        if n == no:
            binary_inter.append(1.0)
        else:
            binary_inter.append(0.0)
    return binary_inter
