code: def clarke_thermalcond(self, structure):
          
          nsites = structure.num_sites
          volume = structure.volume
          tot_mass = sum([e.atomic_mass for e in structure.species])
          natoms = structure.composition.num_atoms
          weight = float(structure.composition.weight)
          avg_mass = 1.6605e-27 * tot_mass / natoms
          mass_density = 1.6605e3 * nsites * weight / (natoms * volume)
          return 0.87 * 1.3806e-23 * avg_mass**(-2./3.) \
              * mass_density**(1./6.) * self.y_mod**0.5
docs: Calculates Clarke's thermal conductivity (in SI units)
  
          Args:
              structure: pymatgen structure object
  
          Returns: Clarke's thermal conductivity (in SI units)