Comment on "Atomic structure and excitation cross section by electron impact of tungsten ions, W$^{38+}$" by El-Maaref et al [J. Phys. B 52(2019) 065202]

Abstract

Recently, El-Maaref et al [J. Phys. B 52(2019) 065202] have reported results for energy levels, radiative rates and collision strengths (Ω) 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 Ω 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 Ω 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.