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Simulations of electron and positron channelling in a crystalline undulatorwith a small amplitude and a short period (A Kostyuk, Phys. Rev. Lett. 110(2013) 115503) were repeated by V G Bezchastnov, A V Korol and A V Solov'yov(J. Phys. B: At. Mol. Opt. Phys. 47 (2014) 195401)for the same parameter setbut using another computer code, MBN Explorer, which implements a differentmodel of projectile scattering by crystal atoms. The authors of the latterpaper claim that their approach, in contrast to the one of the former paper,allows them to observe short-period undulator oscillations in plots ofsimulated trajectories. In fact, the undulator oscillations become visible ontrajectory segments which have a small amplitude of channelling oscillations.This is equally true for both approaches. The claim of Bezchastnov et al. thattheir model is "more accurate" is unfounded. Moreover, there are indications ofsevere mistakes in their calculations: the phases of undulator oscillations inthe trajectories obtained with MBN Explorer are inconsistent with each otherand with well established properties of forced oscillations.

Comment on `Radiation from multi-GeV electrons and positrons in periodically bent silicon crystal'