code: def debye_temperature(self, structure):
          
          v0 = (structure.volume * 1e-30 / structure.num_sites)
          vl, vt = self.long_v(structure), self.trans_v(structure)
          vm = 3**(1./3.) * (1 / vl**3 + 2 / vt**3)**(-1./3.)
          td = 1.05457e-34 / 1.38065e-23 * vm * (6 * np.pi**2 / v0) ** (1./3.)
          return td
docs: Estimates the debye temperature from longitudinal and
          transverse sound velocities
  
          Args:
              structure: pymatgen structure object
  
          Returns: debye temperature (in SI units)