  Weak localization leads to the same correction to both the conductivity and
the McMillan's electron-phonon coupling constant $\lambda$ (and
$\lambda_{tr}$). Consequently the temperature dependence of the thermal
electrical resistivity is decreasing as the conductivity is decreasing due to
weak localization, which results in the decrease of the temperature coefficient
of resistivity (TCR) with increasing the residual resistivity. When $\lambda$
and $\lambda_{tr}$ are approaching zero, only residual resistivity part remains
and gives rise to the negative TCR. Accordingly, the Mooij rule is a
manifestation of weak localization correction to the conductivity and the
electron-phonon interaction. This study may provide a new means of probing the
phonon-mechanism in exotic superconductors.
