def _calc_temp(self, V_a, T0=None):
        if T0 is None:
            T0 = self.eos_mod.refstate.ref_temp()
        # T0, = self.eos_mod.get_param_values(param_names=['T0'], overrides=[T0])
        gamma0, q = self.eos_mod.get_param_values(
            param_names=['gamma0','q'])

        gamma_a = self._calc_gamma(V_a)
        T_a = T0*np.exp(-(gamma_a - gamma0)/q)

        return T_a