Temperature stratification of Tlusty model atmospheres having different model atoms with respect to a fully line-blanketed reference model (No. 5). The shaded region marks the line forming region in the atmosphere. The y-axis shows the temperature difference with respect to the reference model, while the x-axis gives the Rosseland mean optical depth τ_R. The figure demonstrates the effects of metal opacities in NLTE atmospheres. The higher the opacity (the more opacity sources included) the cooler the upper atmosphere and the hotter the deeper layers (surface cooling and back warming).