  In a recent paper Sai {\it et al.} [1] identified a correction $R^{dyn}$ to
the DC conductance of nanoscale junctions arising from dynamical
exchange-correlation ($XC$) effects within time-dependent density functional
theory. This quantity contributes to the total resistance through
$R=R_{s}+R^{dyn}$ where $R_{s}$ is the resistance evaluated in the absence of
dynamical $XC$ effects. In this Comment we show that the numerical estimation
of $R^{dyn}$ in example systems of the type they considered should be
considerably reduced, once a more appropriate form for the shear electron
viscosity $\eta$ is used.
