Gets the thermodynamic Gruneisen tensor (TGT) by via an
        integration of the GGT weighted by the directional heat
        capacity.

        See refs:
            R. N. Thurston and K. Brugger, Phys. Rev. 113, A1604 (1964).
            K. Brugger Phys. Rev. 137, A1826 (1965).

        Args:
            temperature (float): Temperature in kelvin, if not specified
                will return non-cv-normalized value
            structure (float): Structure to be used in directional heat
                capacity determination, only necessary if temperature
                is specified
            quad (dict): quadrature for integration, should be
                dictionary with "points" and "weights" keys defaults
                to quadpy.sphere.Lebedev(19) as read from file

def get_tgt(self, temperature=None, structure=None, quad=None):
        """
        Gets the thermodynamic Gruneisen tensor (TGT) by via an
        integration of the GGT weighted by the directional heat
        capacity.

        See refs:
            R. N. Thurston and K. Brugger, Phys. Rev. 113, A1604 (1964).
            K. Brugger Phys. Rev. 137, A1826 (1965).

        Args:
            temperature (float): Temperature in kelvin, if not specified
                will return non-cv-normalized value
            structure (float): Structure to be used in directional heat
                capacity determination, only necessary if temperature
                is specified
            quad (dict): quadrature for integration, should be
                dictionary with "points" and "weights" keys defaults
                to quadpy.sphere.Lebedev(19) as read from file
        """
        if temperature and not structure:
            raise ValueError("If using temperature input, you must also "
                             "include structure")

        quad = quad if quad else DEFAULT_QUAD
        points = quad['points']
        weights = quad['weights']
        num, denom, c = np.zeros((3, 3)), 0, 1
        for p, w in zip(points, weights):
            gk = ElasticTensor(self[0]).green_kristoffel(p)
            rho_wsquareds, us = np.linalg.eigh(gk)
            us = [u / np.linalg.norm(u) for u in np.transpose(us)]
            for u in us:
                # TODO: this should be benchmarked
                if temperature:
                    c = self.get_heat_capacity(temperature, structure, p, u)
                num += c*self.get_ggt(p, u) * w
                denom += c * w
        return SquareTensor(num / denom)