  We examine an effect of acoustic phonon scattering on an electric
conductivity of single-component molecular conductor [Pd(dddt)$_2$] (dddt =
5,6-dihydro-1,4-dithiin-2,3-dithiolate) with a half-filled band by applying the
previous calculation in a two-dimensional model with Dirac cone [Phys. Rev. B
{\bf 98},161205 (2018)], where the electric transport by the impurity
scattering exhibits the noticeable interplay of the Dirac cone and the phonon
scattering,resulting in a maximum of the conductivity with increasing
temperature. The conductor shows a nodal line semimetal where the band crossing
of HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied
Molecular Orbital) provides a loop of Dirac points located close to the Fermi
energy followed by the density of states (DOS) similar to that of
two-dimensional Dirac cone. Using a tight-binding (TB) model
[arXiv:2008.09277], which was obtained using the crystal structure observed
from a recent X ray diffraction experiment under pressure, it is shown that the
obtained conductivity explains reasonably the anomalous behavior in
[Pd(dddt)$_2$] exhibiting almost temperature independent resistivity at finite
temperatures. This paper demonstrates a crucial role of the acoustic phonon
scattering at finite temperatures in the electric conductivity of Dirac
electrons. The present theoretical results of conductivity are compared with
those of experiments.
