Atomistic modeling of Fe deposition of Mo growth using the BFS method for alloys describes the early stages of the formation of ultrathin Fe films on refractory metal substrates (Mo). Atom-by-atorn analysis and Monte Carlo simulations are used to examine the composition of the islands with increasing Fe coverage. Experimentally known features for submonolayer coverage are successfully reproduced and explained. Beyond 1 ML, simulation results suggest that the stability of the Fe interlayer might be compromised, leading to the formation of islands with mixed composition. (c) 2004 Elsevier B.V. All rights reserved.