The influence of C-defect at Si( 0 0 1) surface on the adsorption and aggregation of different kinds of metal ad-atoms is studied based on total energy and electronic structure density functional theory calculations. It was shown that the formation of C-defect by the dissociative adsorption of water molecule destroys pi bonds in both silicon dimers incorporated into C-defect which leads to the appearance of unsaturated dangling bonds at the free ends of these dimers. The obtained results indicate that this process increases significantly the chemical reactivity of the substrate surface in front of C-defect for three different metallic ad-atoms: Al (III group), Pb (carbon group) and Ag (transition metal). It was shown that the increase of the adsorption energy in the vicinity of C-defect can initiate the process of aggregation of ad-atoms diffusing on silicon substrate. (C) 2014 Elsevier B.V. All rights reserved.