code: def get_phonon_frequencies(self):
          
          # TODO: the following is most likely not correct or suboptimal
          # hence for demonstration purposes only
          frequencies = []
          for k, v0 in self.data.iteritems():
              for v1 in v0.itervalues():
                  vec = map(abs, v1['dynmat'][k - 1])
                  frequency = math.sqrt(sum(vec)) * 2. * \
                              math.pi * 15.633302  # THz
                  frequencies.append(frequency)
          return frequencies
docs: calculate phonon frequencies