  The snapshot model of crystal atoms was implemented in the Monte Carlo code
ChaS (Channeling Simulator) and is being successfully used for simulation of
ultrarelativistic particle channeling. The model was criticized by Sushko et
al. (J. Comp. Phys. 252 (2013) 404-418) who claim that it overestimates the
mean scattering angle in a single projectile-atom collision. As a matter of
fact, no evidence that would support this claim can be found in the mentioned
publication. Moreover, the snapshot model and the model suggested by Sushko et
al. yield essentially the same value of the mean scattering angle. Contrary to
the claim of Sushko et al., the target electrons can be considered as
fixed-position scatterer, corrections due to their finite mass and nonzero
initial velocity have a negligible impact on the channeling of light
projectiles (electrons and positrons). In contrast to the snapshot model, the
model preferred by Sushko et al. does not take into account incoherent
scattering of the projectile by crystal electrons. This explains why the two
models predict different values of the dechanneling length. The claim that the
snapshot model underestimates the dechanneling length is unfounded. In actual
fact, this model is in good agreement with experimental data.
