Concerning the microscopic linear response theory

We present a procedure for dealing with the fluctuation–dissipation theorem (Kubo) without using Liouville–Neumann phase-space evolution. Thus, our procedure clarifies some objections posed against microscopic linear-response theory. As an application of our method, we revisit the calculation of the electric conductivity, in particular emphasis is made to establish the validity of the Greenwood–Peierls DC-conductivity when compared with the fundamental Kubo's formula.