In our Comment we question the validity of the claim made by the authors of \cite{cc} that their solutions of the Dirac equation in an external {\em time-dependent} electromagnetic field describe beams of electrons. In every time-dependent field, no matter how weak, which has {\em infinite} time duration, there is a continuous electron-positron pair creation and annihilation. Without the proper accounting for these processes, the mathematical solutions of the Dirac equation are not directly applicable to realistic physical situations. In particular, the time evolution of the average values $\langle x\rangle$ and $\langle y\rangle$ does not describe the electron trajectory but the motion of some combination of the electron and positron charge distributions with pathological properties (zitterbewegung).
Comment on " Solutions of Dirac equation with an improved expression of the Rosen-Morse potential energy model including Coulomb-like tensor interaction"
Comment on "Position-dependent effective mass Dirac equations with PT- symmetric and non - PT- symmetric potentials" [J. Phys. A: Math. Gen. 39 (2006) 11877--11887]
Derivation of the magnetization current from the non-relativistic Pauli equation: A comment on "The quantum mechanical current of the Pauli equation" by Marek Nowakowski [Am.J.Phys.67(10), 916-919 (1999)]
A possible correspondence between Ricci identities and Dirac equations in the Newman-Penrose formalism: towards an understanding of gravity induced collapse of the wave-function?
