the new APOGEE MARCS, APOGEE Kurucz, and earlier (NEWODF) Castelli-Kurucz models [@castelli01], respectively. While the APOGEE Kurucz and MARCS models share essentially the same chemical composition [@asplund01; @grevesse02], the Castelli-Kurucz models use the solar mixture given by @grevesse01.

For both the cooler (red line) and the warmer model (blue line), we see good agreement between the MARCS and the ATLAS9 models presented in this paper. The new MARCS and ATLAS9 models show good agreement, the differences are modest, less than 1 percent, for the thermal structure, and less than 2$-$3 percent for the gas pressure and the electron density in the layers where weak spectral lines and continuum form ($\tau >$ 0.01). These small differences are most likely related to the different equation of state implemented in the two codes, and can also be due to the fact that ATLAS9 uses the ODF method, while MARCS uses the OS method. The differences between the two increase at temperatures lower than 4000K due to the different H$_{2}$0 and TiO linelists used in the calculations. More importantly, larger differences are present in the gas pressure and electron density in the ATLAS9 models compared to the Castelli-Kurucz ones for the cooler models. These 