Growth mechanism of carbon nanotubes (CNT) on nickel nanoparticles has been investigated using a multiscale modeling approach that integrates density functional theory (DFT) calculations and Kinetic Monte Carlo (KMC) simulations. The proposed elementary steps that control the catalytic CNT growth were first analyzed using DFT. The energetic results were then used to build an intrinsic kinetic database that was incorporated into a novel KMC framework that has been developed to overcome large disparities in time scales for this system. KMC simulations show that CNT growth is dominated by the surface diffusion of carbon species. Moreover, it was found that the surface diffusion of the small carbon cluster, e.g., trimer, is a critical step in the growth mechanism of the CNT since it prevents further nucleation of the C atoms on the catalyst surface, and therefore inhibits the deactivation of the catalyst. The CNT growth rates predicted by the KMC simulations agree reasonably well with experimental data, verifying the proposed CNT growth mechanism and KMC model. (C) 2015 Elsevier Inc. All rights reserved.