Crystal growth of GaN by hydrogen vapor phase epitaxy (HVPE) is still far from being described on the atomic level. The method consists of reaction of HCl with liquid Ga, transport of gallium by volatile compounds GaCl or GaCl3, and the deposition on the substrate by the simultaneous reaction of GaCl/GaCl3 and ammonia (NH3) on the GaN surface. Various aspects of the method have to be modeled using different approaches. Recently, we have modeled reaction of HCl with gallium and the transport of the resulting species by convection and diffusion using CFD modeling of transport. Surface reaction rate was estimated using atomic flux and sticking coefficient. It has been found that the reaction is controlled by transport or surface reaction depending on the flow velocity and the HCl sticking coefficient [P. Kempisty, I. Grzegory, M. Bockowski, S. Krukowski, B. Lucznik, B. Pastuszka, S. Porowski, Phys. Stat. Sol. (a) 203 (2006) 131; P. Kempisty, I. Grzegory, M. Bockowski, S Krukowski, B. Lucznik, B. Pastuszka, S. Porowski, J. Crystal Growth 296 (2006) 31]. The growth of GaN was modeled using atomistic scale simulations. The simulations were carried out using the QM DFT SIESTA code [J.M. Soler, E. Artacho, J.D. Gale, Alberto Garcia, J. Junquera, P. Ordejon, D. Sanchez-Portal, J. Phys.: Condens. Matter 14 (2002) 2745; P. Ordejon, D.A. Drabold, M.P. Grumbach, R.M. Martin, Phys. Rev. B 48 (1993) 14646; P. Ordejon, D.A. Drabold, M.P. Grumbach, R.M. Martin, Phys. Rev. B 51 (1995) 1456]. The model is applied to a 2-d supercell, which corresponds to 2-d periodic boundary conditions suitable for simulation of the surface. Five atomic slabs were used in the direction perpendicular to the surface. The simulations include the analysis of the influence of hydrogen, ammonia and HCl on the atomic structure of the (0 0 0 1) GaN surface (Ga-face). Subsequently, the process of adsorption of various species, such as NH3, GaCl and H, of the GaN(0 0 0 1) surface, was considered. The energy barriers and the stable configurations were obtained. From this, the energetic properties of elementary kinetic processes were obtained. These results were used for the assessment of the influence of the growth conditions on the growth rate of gallium nitride. (C) 2007 Elsevier B.V. All rights reserved.