In order to explore the interfacial structure of Mg/Al4C3 interface and clarify the heterogeneous nucleation potential of Al4C3 particles in Mg melt. The atomic structure, bonding, and interfacial energy of Mg/Al4C3 interfaces were studied by first-principles calculations to analyze the sequence of Mg atoms onto the surface of Al4C3 (0 0 0 1) slab. Surface energy calculations show that the outmost layer of Al4C3 free surface having a preference of C atom termination. And polar covalent/ionic mixed bonds are formed across interface during the combination of Mg atoms with C-terminated Al4C3 surface. The calculated interfacial energy of Mg/Al4C3 interface is much smaller than that between alpha-Mg and magnesium melts, proving the excellent nucleation potency of Al4C3 particles for alpha-Mg grains from interfacial atomic structure and atomic bonding energy considerations. (c) 2013 Elsevier B.V. All rights reserved.