  We proposed in an earlier paper [arXiv:1108.6141] an empirical formula of the
electrical conductivity which agrees with experiments within 20 percent for the
most of pure elemental metals at room temperature ranges. This is obtained, in
Drude formula, by replacing the electron density with the number density of
atoms n(atom), and the electron effective mass with true electron mass
multiplied by G. Here the relaxation time is assumed to be (h/2pi)/(kT) for all
metals (h is the Planck constant and k is the Boltzmann constant). The single
free parameter G is summed electron numbers in each atomic shell, e.g. G=5+1=6
for chromium(five 3d electrons and one 4s electron). In this paper, we find
that the above relaxation time can be reproduced if the autocorrelation time of
electron fluctuating velocity in a simple fluctuation dissipation theorem is
converted to 2delta(energy)delta(time)/kT, and if this delta(energy)delta(time)
is assumed equal to (h/2pi)/2 of the Heisenberg's minimum uncertainty. This
corresponds to the closest approach, or head-on colliisions. Independent from
this, we find that n(electron)=n(atom), is appropriate for the conductivity in
most elemental metals. In discussing the 5th power temperature dependence of
resistivity, we find that, besides the use of the Debye temperature unit, the
temperature unit defined by the ion plasma frequency times (h/2pi)/k is equally
acceptable. Here the ion plasma frequency is only depending on n(electron)
unlike somewhat ambiguous Debye temperature.
