In order to learn more about nitrogen incorporation during in situ doping, adsorption of nitrogen-containing species onto the SiC(0001) surfaces has been theoretically investigated using DFT calculations under periodic boundary conditions. As a guide to the composition of gaseous species above a growing SiC surface, earlier results from thermodynamic calculations, performed at experimental conditions for N in situ doping, were regarded. The present results show that one- and two-fold adsorption of N-2, N, NH3, HCN and HNC to the SiC surfaces is generally exothermic. The exceptions include one-fold adsorption (by the N atom) of NH3, HCN and HNC to the C surface. Furthermore, the adsorbates were found to bind stronger by the N atom to the Si surface while adsorption by the C atom was similar in strength to both surfaces. The adsorption processes were generally found to be energetically more favorable for the Si surface and structurally slightly more favorable for the C surface.