The bulk and (0 0 1) surface of chalcopyrite have been investigated using Plane Waves Density Functional calculations. The band structure and the optimized lattice parameters are in good agreement with previously published results. The relaxed S-terminated (0 0 1) surface led to the formation of disulphide, S-2(2-), upon the reduction of Fe(III) to Fe(II). The relaxed M-terminated (0 0 1) surface led to the formation of metal sulphides and metal-metal bonds. The calculated Fe-Fe, Fe-Cu and Cu-Cu bond lengths are close to the typical bond distances found in the metal. Lowdin population analysis, density of states and electron localization function have been used to understand the electronic structure of the chalcopyrite surfaces. Implications to the chalcopyrite surface reactivity are briefly discussed. (C) 2010 Elsevier B.V. All rights reserved.