The AlB2(1 1 1) surfaces and Al(1 1 1)/AlB2(0 0 0 1) interface were studied by first-principles calculations to clarify the heterogeneous nucleation potential of alpha-Al grains on AlB2 particles in purity aluminium and hypoeutectic Al-Si alloys. It is demonstrated that the AlB2 (0001) surface models with more than nine atomic layers exhibit bulk-like interior, wherein the interlayer relaxations localized within the top three layers are well converged. The outmost layer of AlB2 free surface having a preference of metal atom termination is evidenced by surface energy calculations. With Al atoms continuing the natural stacking sequence of bulk AlB2, Al-Al metallic bonds are formed across interface during the combination of Al atoms with Al-terminated AlB2 surface. The calculated interfacial energy of the Al/AlB2 interface is much larger than that between the alpha-Al and aluminium melts, elucidating the poor nucleation potency of alpha-Al grains on AlB2 particles from thermodynamic considerations. (C) 2011 Elsevier B. V. All rights reserved.