Density functional theory calculations have been performed on the structure and stability of Fe4C bulk and the corresponding low-index surfaces. It is found that the structure with octahedral interstitial carbon (Fe4C/oct) is more stable than that with tetrahedral interstitial carbon (Fe4C/tet). For Fe4C/oct, the most stable surface termination is the (100) surface with mixed carbon and iron (T-Fe/C). For Fe4C/tet, the most stable surface termination is the dramatically reconstructed (110) surface with the newly formed T-Fc/C surface layer. (c) 2007 Elsevier B.V. All rights reserved.