Recently, El-Maaref { \it et al}\, [J. Phys. B 52(2019) 065202] have reported results for energy levels, radiative rates and collision strengths ($\Omega$) for some transitions of Kr-like W~XXXIX. For the calculations of these parameters they have adopted several codes, including GRASP, DARC and FAC. For energy levels they have shown discrepancies of up to 1.64~Ryd between the GRASP and FAC calculations, whereas for $\Omega$ the differences between the DARC and FAC results are over an order of magnitude for a few transitions. In addition, for several transitions there is an anomaly in the behaviour of $\Omega$ between the two sets of calculations. In this comment, we demonstrate that their results from both codes are incorrect, and hence cannot be relied upon.
Categories: physics.atom-ph