A primitive cell is searched in the input cell. When a primitive
    cell is found, an object of Atoms class of the primitive cell is
    returned. When not, None is returned.

def find_primitive(cell, symprec=1e-5):
    """
    A primitive cell is searched in the input cell. When a primitive
    cell is found, an object of Atoms class of the primitive cell is
    returned. When not, None is returned.
    """
    lattice, positions, numbers = spg.find_primitive(cell.totuple(), symprec)
    if lattice is None:
        return None
    else:
        return Atoms(numbers=numbers,
                     scaled_positions=positions,
                     cell=lattice,
                     pbc=True)