def getvqpoints(self, q):
        self.generate_vqconf(q)
        passthru(config.phonopy + "--tolerance=1e-4  q.conf")
        data = parseyaml('qpoints.yaml')
        file = open("v.txt", 'w')
        for phonon in data['phonon']:
            qp = phonon['q-position']
            for band in phonon['band']:
                frequency = band['frequency']
                v = np.array(band['group_velocity'])
                v = np.linalg.norm(v)
                print >> file, "%s\t%f\t%f" % ('\t'.join(map(str, qp)),
                                               frequency, v)
        file.close()
        v = np.loadtxt('v.txt')
        plot(
            (v[:, 3], 'Frequency (THz)'), (v[:, 4],
                                           'Group Velocity (Angstrom/ps)'),
            'v_freq.png',
            grid=True,
            scatter=True)