def check1(self, filename='FORCE_CONSTANTS'):
        ref = io.read('SPOSCAR')
        fc2 = readfc2(filename)
        np.set_printoptions(precision=2, suppress=True)
        files = ['dir_POSCAR-001']
        vasprunxml = "dir_SPOSCAR/vasprun.xml"
        if exists(vasprunxml):
            vasprun = etree.iterparse(vasprunxml, tag='varray')
            forces0 = parseVasprun(vasprun, 'forces')
            print(forces0.max())
        else:
            forces0 = 0.0
        for file in files:
            print(file)
            POSCAR = 'dirs/%s/POSCAR' % file
            vasprunxml = "dirs/%s/vasprun.xml" % file
            atoms = io.read(POSCAR)
            u = atoms.positions - ref.positions
            f = -np.einsum('ijkl,jl', fc2, u)

            vasprun = etree.iterparse(vasprunxml, tag='varray')
            forces = parseVasprun(vasprun, 'forces') - forces0
            print(np.abs(f).max(), "\n")
            print(np.abs(forces - f).max())
            print(np.allclose(f, forces, atol=1e-2))