Left: relation between the Ne23 parameter and the total oxygen abundance for the subset of models with log(N/O) = −0.625 dex. Right: relation between the Ne2Ne3 parameter and log U. O/H and log U shown in these figures for the local star-forming galaxies (purple circles: dwarf galaxies; red triangles: nearby starbursts; green squares: local LIRGs) are derived from the optical emission lines using HCM, and are compared with the IR parameters Ne23 and Ne2Ne3, respectively, that were measured in the IR spectra. A polynomial fit to the O/H values for the whole grid of models is also shown (dashed black line in the left panel; see Eq. (3)).