code: def get_nac_frequencies_along_dir(self, direction):
          
          versor = [i / np.linalg.norm(direction) for i in direction]
          for d, f in self.nac_frequencies:
              if np.allclose(versor, d):
                  return f
  
          return None
docs: Returns the nac_frequencies for the given direction (not necessarily a versor).
          None if the direction is not present or nac_frequencies has not been calculated.
  
          Args:
              direction: the direction as a list of 3 elements
          Returns:
              the frequencies as a numpy array o(3*len(structure), len(qpoints)).
              None if not found.