Calculates Clarke's thermal conductivity (in SI units)

        Args:
            structure: pymatgen structure object

        Returns: Clarke's thermal conductivity (in SI units)

def clarke_thermalcond(self, structure):
        """
        Calculates Clarke's thermal conductivity (in SI units)

        Args:
            structure: pymatgen structure object

        Returns: Clarke's thermal conductivity (in SI units)

        """
        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