To investigate the surface energy anisotropy of carbon-adsorbed iron surfaces related to carbon nanotube growth we have performed self-consistent pseudopotential density-functional calculations. The iron particle's equilibrium shape is obtained from the Wulff construction using the calculated surface energies. We investigate the adsorption and diffusion of carbon atoms on the iron surfaces. It is found that the desorption energy of the carbon atoms and the activation energy for carbon diffusion are very different on different facets. Using the energetics of carbon-adsorbed iron surfaces, we evaluate the formation energies of the surfaces as a function of carbon chemical potential. Since the surface energies of the low-index iron facets are affected differently by the presence of carbon, the crystal shape is changed correspondingly. (C) 2003 Published by Elsevier B.V.