code: def trans_v(self, structure):
          
          nsites = structure.num_sites
          volume = structure.volume
          natoms = structure.composition.num_atoms
          weight = float(structure.composition.weight)
          mass_density = 1.6605e3 * nsites * weight / (natoms * volume)
          if self.g_vrh < 0:
              raise ValueError("k_vrh or g_vrh is negative, "
                               "sound velocity is undefined")
          return (1e9 * self.g_vrh / mass_density) ** 0.5
docs: Calculates transverse sound velocity (in SI units) using the
          Voigt-Reuss-Hill average bulk modulus
  
          Args:
              structure: pymatgen structure object
  
          Returns: transverse sound velocity (in SI units)