def test_vacancy():
    from ase import Atoms
    from ase.optimize import QuasiNewton
    from ase.neb import NEB
    from ase.optimize.mdmin import MDMin
    try:
        from asap3 import EMT
    except ImportError:
        pass
    else:

        a = 3.6
        b = a / 2
        initial = Atoms('Cu4',
                        positions=[(0, 0, 0),
                                   (0, b, b),
                                   (b, 0, b),
                                   (b, b, 0)],
                        cell=(a, a, a),
                        pbc=True)
        initial *= (4, 4, 4)
        del initial[0]
        images = [initial] + [initial.copy() for i in range(6)]
        images[-1].positions[0] = (0, 0, 0)
        for image in images:
            image.calc = EMT()
            #image.calc = ASAP()

        for image in [images[0], images[-1]]:
            QuasiNewton(image).run(fmax=0.01)
        neb = NEB(images)
        neb.interpolate()

        for a in images:
            print(a.positions[0], a.get_potential_energy())

        dyn = MDMin(neb, dt=0.1, trajectory='mep1.traj')
        #dyn = QuasiNewton(neb)
        print(dyn.run(fmax=0.01, steps=25))
        for a in images:
            print(a.positions[0], a.get_potential_energy())
