def METHOD_NAME(element_a, element_b, a=None):
    """
    Builds a cubic $AB$ B2 structure of interpenetrating simple cubic lattices.
    Args:
        element_a (str): The chemical symbol for the A element.
        element_b (str): The chemical symbol for the B element.
        a (float): The lattice constant. (Default is None, which uses the default for element A.)
    Returns:
        (Atoms): The B2 unit cell.
    """
    return ase_to_pyiron(METHOD_NAME(element_a=element_a, element_b=element_b, a=a))