3.3.6 Different sets of relevant observables

After fully linearizing the statistical operator (161) with (155), we have for the electrical current density

$$\langle \mathbf{j}\_{\rm el} \rangle = \frac{e}{m\Omega} \langle \mathbf{P} \rangle = \frac{e\beta}{m\Omega} \left\{ \sum\_{n} \left[ (\mathbf{P}|\mathbf{B}\_{n}) - \langle \mathbf{P}; \dot{\mathbf{B}}\_{n} \rangle\_{ie} \right] F\_{n} + \langle \mathbf{P}; \mathbf{P} \rangle\_{ie} \frac{e}{m} E \right\} = \sigma\_{\rm de} E. \tag{182}$$

After deriving the Ziman formula from the force-force correlation function in the previous section, we investigate the question to select an appropriate set of relevant observables Bf g<sup>n</sup> .
