1.5K during two consecutive iterations. Occasionally convergence takes longer, and some models do not converge at all. A converged model with similar model parameters is then identified as a new starting model. This approach is often successful, but some models do not converge, which leaves vacancies in the model grid.

Discussion
==========

Changes in the chemical composition can have a number of effects on the calculated atmospheres. These effects are mainly related to either changes in opacity or changes in the equation of state. The main effect of an increased line opacity in late-type stars is either cooling or warming (depending on the opacity and its wavelength dependence) of the outer layers and also back-warming of the innermost ones [@gustafsson01]. Changes in the equation of state are mainly variations in the mean molecular weight for abundant elements, changes in the number of free electrons for elements that are important electron donors, or other more intricate changes related to chemical equilibrium through molecule formation. In the next two sections, we give examples of MARCS and ATLAS9 models from our grid, and illustrate briefly the changes in the model atmospheres related to large changes in C and $\alpha$ elements.

![Examples of ATLAS9 