column_density

Define model column density, $N$. Units are cm$^{-2}$. This quantity is used in calculation of thickness of model slab according to $\Delta R_{max}=N/n$ where n is the density or an estimate based on pressure and temperature initial values. The default value for N is $10^{21}$ cm$^{-2}$. The model calculation terminates when this value is reached.