def METHOD_NAME(alat):
    """
    Set up Si primitive cell
    fcc Si:
       alat
       0.5000000000000000    0.5000000000000000    0.0000000000000000
       0.0000000000000000    0.5000000000000000    0.5000000000000000
       0.5000000000000000    0.0000000000000000    0.5000000000000000
    Si
       1
    Cartesian
    0.0000000000000000  0.0000000000000000  0.0000000000000000
    """
    structure_data = DataFactory('structure')
    lattice = np.array([[.5, .5, 0], [0, .5, .5], [.5, 0, .5]]) * alat
    structure = structure_data(cell=lattice)
    for pos_direct in [[0.0, 0.0, 0.0]]:
        pos_cartesian = np.dot(pos_direct, lattice)
        structure.append_atom(position=pos_cartesian, symbols='Si')
        structure.label = f"silicon_at_{str(alat).replace('.', '_')}"
    return structure