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The approximate methods to calculate the diffuse ionizing radiation (DIR) during the photoionization modelling (PhM) of the nebular environments are frequently used with purpose to increase the calculation speed of modern photoionization codes as well as for simplification of their calculation algorithms. The most popular Outward Only method in many cases gives the satisfactory calculation precision and speed. However, in our previous studies it was shown that even for nebular environments with constant density the calculation errors, related to usage of approximate method of DIR, are significant for spatially extended or optically thin objects. However, constant density is a bit rough assumption. In present work to compare the detailed method of DIR calculation with Outward Only one we used more realistic density distribution for planetary nebulae proposed by Golovatyy & Mal’kov. Using optimal photoionization models for IC 5117 and NGC 7293, obtained by Melekh et al. and calculated in Outward Only approximation, we recalculated them using detailed method of DIR calculation. While IC 5117 is the most compact (young) and dense planetary nebula from sample used by Golovatyy & Mal’kov, NGC 7293 is the most extended (old) with lowest density one from the same sample.

We compared PhM results for these PNe obtained using Outward Only approximation and detailed method of DIR treatment. It was concluded that largest differences in ionization structure of nebula caused by differences in DIR calculation methods are in outer part of PN - at radii larger than maximal density radius. Therefore, [N II], [O II] and [S II] and other emission lines, that achieve the maximal emissivities in outer part of PNe, are the most sensitive to DIR calculation method.