  In their work, Yan et al. [Phys. Rev. B 88, 121403 (2013)] employing density
functional perturbation theory (DFPT) calculations, demonstrate that silicene
and germanene show weaker Kohn anomalies in the $\Gamma$-$E_g$ and $K$-$A_1$
phonon modes, compared to graphene. Furthermore, they compute the electron
phonon (e-ph) coupling matrix elements using the frozen phonon approach and
found that in silicene the average e-ph coupling matrix-element square over the
Fermi surface, $\langle g_{{\bf q}\nu}^2\rangle_{F}$, is about 50 % of those in
graphene, but in germanene is weaker and nearly negligible. However, Yan et al.
argues that the smaller Fermi velocity in silicene compensates the reduced
$\langle g_{{\bf q}\nu}^2\rangle_{F}$, leading to phonon linewidths
($\gamma_{{\bf q}\nu}$) slightly larger than those in graphene. In this
Comment, we show that the DFPT and the frozen phonon results of Yan et al. for
silicene are inconsistent. Additionally, we have evaluated the e-ph coupling
using direct DFPT calculations, analytical relations, and frozen phonon
calculations, and we found systematically that $\langle g_{{\bf
q}\nu}^2\rangle_{F}$ and $\gamma_{{\bf q}\nu}$ in silicene are one order of
magnitude smaller than in graphene, in contrast to the conclusions of Yan et
al.
