Theory of electron transport in disordered systems: the nearly free-electron and nearly bound-electron limits

Electron dynamics in a liquid metal is studied in the nearly free-electron and nearly bound-electron limits including in both cases coupling of the electron motion to collective translational excitations of the ion-core fluid. The kinetic equations descriptive of both limits are of Boltzmann form provided that the fluctuations in the band width are smaller than the bandwidth and that the bandwidth is larger than the average phonon frequency. The translational excitations of the ion-core fluid lead to extra temperature dependences of the transport coefficients. In the nearly free-electron limit this contribution is small and the Ziman theory is recovered. In the nearly bound-electron limit the contribution to the temperature dependence of, say, the conductivity by coupling to translational excitations of the ion-core fluid is important.